This PDF file contains the front matter associated with SPIE Proceedings Volume 10934, including the Title Page, Copyright Information, Table of Contents, Introduction, and Author and Conference Committee lists

A simple composite cavity fiber tip (CCFT) Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated. The composite cavity is composed of an air cavity and a silica cavity. The air cavity is an elliptical air hole embedded in the SMF. The silica cavity is a short section of SMF cascaded to the air cavity. The CCFT FPIs were applied for temperature sensing. To take advantage of the FP’s resonant property, a laser whose wavelength is tuned to the steep slope of one of the FP resonances is used to interrogate the CCFT FPI system. With a laser interrogation, a small wavelength shift caused by a small temperature change will then be translated into a large change in output power, which can be easily detected. Therefore, the temperature sensitivity can be enhanced significantly, and the CCFT FPI can routinely resolve much smaller temperature changes.

Measurement and monitoring of geomagnetic field in the mesosphere has many potential applications such as detection of oceanic currents, mapping of large-scale magnetic structures, and study of electric-current fluctuations in the ionosphere. Remote measurement of the geomagnetic field can be performed by optical pumping of sodium atoms in the mesosphere with an amplitude modulated (AM) light at the Larmor precession frequency, and observing the magnetic resonance in fluorescence at a ground station. In this context, we have conducted an experiment in the laboratory to demonstrate remote magnetic field measurement using fluorescence signal from a sodium cell. Sodium atoms in the cell are interrogated with AM light produced by an acousto-optic modulator (AOM), introduced in the beam path of a frequency-doubled amplified sodium laser made in our laboratory. Magnetic resonance observed in sodium cell fluorescence is studied as a function of varying magnetic field intensity. Characteristics of the magnetic resonance such as linewidth and contrast (or SNR), and their dependence on optical power density, AM duty cycle, B-field orientation and intensity are studied. Theoretical modeling and experimental measurements are also carried out to determine the sensitivity of the magnetometer for realizing remote magnetometry with mesospheric sodium atoms.

Resonant excitation of an atomic medium with amplitude modulated (AM) light can produce synchronous optical pumping effects. Nonlinear magneto-optical rotation (NMOR) is produced with AM light when the optical pumping rate is synchronous with the Larmor frequency. Traditionally, magnetic field measurements have been performed using lock-in detection of the NMOR signal with the transmitted light. Instead of NMOR, we have studied intensity correlation between two orthogonally polarized components of the AM light passing through a rubidium vapor cell, for magnetic field measurements. We have used a pure 87Rb cell (1 cm in diameter and 2 cm in length) filled with Ne buffer gas for this study. Intensity correlation is performed by recording the intensity data from two fast photodetectors with a high bandwidth digitizer board. We have measured the dependence of the zero-delay intensity correlation on the magnetic field. We have also studied the dependence of the correlation width on the light intensity and cell temperature. Results obtained from the theoretical model are also compared with the experiment. The results suggest intensity correlation can be used as a viable technique for improving the performance of magnetic field measurements with AM light.

See above

We have shown that Rydberg states can be used for high-sensitivity, absolute sensing of microwave (MW) electric fields. We achieved a sensitivity of 3 μVcm^-1Hz^-1/2 for two read-out strategies. Depending on the spectral resolution of the read-out, either the MW induced transmission line frequency splitting, the Autler-Townes regime, or a change in the on-resonant absorption, the amplitude regime, can be used to determine the MW electric field. Results using a Mach-Zehnder interferometer and frequency modulated spectroscopy both achieve similar photon shot noise limited sensitivity. In addition, we have also explored amplitude modulation and the displacement of a probe laser beam due to index of refraction changes in a prism shaped vapor cell. These latter methods were not able to achieve photon shot noise limited performance. Fundamental limits to the sensitivity of the Rydberg atom-based MW electric field sensing have been addressed, but it is important to clarify the differences between noise in different parts or subsystems of the sensor. Shot noise in the probe laser usually dominates the projection noise of the atoms participating in the measurement of the MW electric field because of the desire to operate at low effective Rydberg atom densities in order to avoid collisional dephasing and ionization.

A highly sensitive temperature sensor based on an isopropanol-sealed optical microfiber coupler (OMC) is proposed and investigated. Isopropanol is a kind of material with high thermo-optic coefficient. By encapsulating the OMC into isopropanol environment, the OMC can be turned to a highly sensitive temperature sensor. Using this approach, we experimentally demonstrate a temperature sensor. By optimizing the waist diameter of the OMC, an ultrahigh temperature sensitivity of -5.89 nm/° has been achieved at the waist diameter of 2.2 μm in the range of 30-40°.

Refractive index describes the speed of light originating from light-matter interaction in its most linear form. Differently, the imaginary index defines nonlinear gain and alternating its sign allowed nonreciprocity. Yet, linear nonreciprocity by irreversible index, like in downstream literally dragging light (Fizeau, 1851), was never considered. As spinning devices isolate sound (Alù, 2014), one might ask why such a simple and straightforward approach was not considered for photonics applications such as optical isolation? The major technology stopper corresponds to maintaining separation between spinning cavities and couplers within tolerance-ranges of as small as several nanometers, as needed for critical coupling. But since light travels faster than sound, speeds near 360 km/hr are needed inside the resonator for isolating light. However, resonators spinning at 400,000 RPM for achieving such velocities, results in an un-tolerated wobbling, making coupling18,19 challenging. Inspired by harddrive technology of heads aerodynamically flying above disks. Here, we fabricate photonic couplers flying at nano-elevation over resonators spinning fast enough to fully split their counter-circulating optical-modes; and experimentally demonstrate that a coupled fiber turns transparent from one side, while at the same time, opaque from its other end. In the past, near zero-drag20 gas-film lubricantion21 enabled the big-data revolution22. This principle benefits here self-adjusted photonic flyers permitting 99.6% isolation in standard telecom fibers. Unlike flat geometries, the saddle-convex geometry of our bent-nanowire and sphere makes them relatively easy to bring closer; which might impact surface-science studies at nano-separations, where Casimir- and van der Walls-forces dominate, and gravity might even be examined.

Frequency combs are revolutionizing metrology, providing a link between optical and RF fre- quencies. The cavity of a mode-locked laser determines the wavelength of a particular comb tooth, and the teeth spacing. It is demonstrated experimentally that the average tooth spacing of a frequency comb can be tuned by tilting an etalon inserted in the cavity. This pro- perty amounts to a control of the average group velocity of a pulse circulating in the resonator. We have shown that a mode-locked laser in which two pulses circulate constitutes a sensitive phase sensor. This is because any phase shift between the two pulses is converted into a frequency shift, equal to the ratio of the phase shift to the cavity round-trip time at the phase velocity. The two frequency combs issued from the laser are split in frequency, a split measured as a beat note on a detector recording the interfering combs. A laser gyro is an example of such an Intracavity Phase Interferometer. A structure with periodic discrete resonances matching several teeth of the comb will, because of the dispersion associated with the resonances, decrease or increase the beat note, since the split combs will see different cavity round-trip times. Such reso- nant structures that applies to multiple teeth of the comb can be passive resonators (Fabry-Perot) in transmission or reflection, narrow atomic two-photon resonances, phase matched frequency dou- blers, etc. . . . Experimental demonstrations will be presented. No correlation is observed between pulse velocity and beat note enhancement/reduction.

Abstract Not Submitted

Intracavity phase interferometry (IPI) is a highly sensitive technique, using mode-locked lasers with two counter-propagating pulses, to measure small displacements, linear and nonlinear refractive indices, magnetic field, scattering, rotation and acceleration. Inertial sensors are needed for high accuracy navigation. Although gyroscopic response was successfully realized in discrete element mode-locked lasers with two circulating pulses, it is impractical in commercial systems. Fiber lasers are the most promising systems to implement IPI, owing to the possibility of producing ultrashort pulses with a compact and low-cost design. There are however substantial challenges to transfer the results of discrete optics lasers to fibers. Most publications on bidirectional fiber lasers report a different average group velocity for each of the circulating pulses, a situation rendering IPI impossible. This problem was solved by constructing an all-PM bidirectional mode-locked fiber laser with two portions of Er-doped fibers pumped through two WDMs to eliminate all the asymmetries in the cavity. In addition to ensuring equal group velocity for each pulse, the symmetric operation reduces the bias beat note. A fine control of the bias is obtained by tuning the pump powers of the two gain sections, in order to minimize the difference between the nonlinear phase accumulated in each direction between absorber and output coupler. Another challenge is to minimize the dead band created by the large scattering of the carbon nanotube. The solution that we implement is to force one of the intracavity pulses to propagate along the fast axis, the other along the slow axis.

Detection of fast optical phase modulation is a critical procedure in different areas of modern optical technology. Conventional homodyne detection technique needs mixing with the local oscillator, or with the reference wave, phase-locked with the detected wave with the quadrature phase difference (+/-)Pi/2 for linear demodulation. Additional complications appear from the necessity to ensure similarity of polarizations of these two light-waves and their complicated wave-fronts in case of detection of the light reflected from a rough inspected surface. All these problems can be solved in the self-reference configuration based on confocal Fabri-Perot cavity, but it is complicated and needs frequency-locking with the detected wave. We propose utilization of phase memory of an ensemble of acetylene molecules (C2H2) vibration-rotational transitions for a self-reference homodyne detection of sub-ns optical phase modulation in 1520-1540nm wavelength range. In the reported configuration, the collinearly propagating dipole radiation of the excited by the incident light two-level centers acts like the coherent properly phased reference wave necessary to transform the phase modulation into the intensity one. It is experimentally demonstrated in the optical fiber compatible hollow-core photonic crystal fiber cell filled with the 0.4Torr gas at 1530nm wavelength of the acetylene P9 absorption line at the sub-mW scale cw power. The response to the detected phase modulation was quadratic when the acetylene inhomogeneous absorption line was excited in its center but was linearized by tuning to one side of the absorption line. Similar self-reference detection of the multimode wavefronts is also possible in the bulk gas cells.

Abstract not submitted

We review the latest developments in long-range Brillouin optical time-domain analysis sensors. The factors that impair the performance of these sensors, particularly in terms of their distance range, are discussed together with the latest methods to overcome them. We focus on our recent contributions based on the application of the probe dithering method, which is based on introducing a wavelength modulation to the probe wave. This technique is shown to effectively compensate nonlocal effects originated in the depletion of the pump pulse as well as of its pedestal. In addition, it can provide amplification to the pump wave with a slight modification of the setup. Furthermore, this method can be combined with pump pulse coding and a new technique for coding linearization that we have devised to further extend the sensing length into the hundreds of kilometers range.

We report loading of laser-cooled caesium atoms into a hollow-core photonic-bandgap fiber and confining the atoms in the fiber’s 7μm diameter core with a red-detuned dipole trap. In this system, the atom-photon interaction probability is in the range of 0.5% and optical depths exceeding 100 can be achieved. We discuss the outlooks for photon storage and nonlinear optics at low light levels, such as cross-phase modulation and single-photon wavelength conversion, in this system.

Abstract not submitted

The study of quantum many-body spin physics in realistic solid-state platforms has been a long-standing goal in quantum and condensed-matter physics. We demonstrate separate steps required to reach this goal using nitrogen-vacancy (NV) centers in diamond. First, standard (TEM) electron irradiation is used for the enhancement of N to NV conversion efficiencies by over an order-of-magnitude. Second, robust pulsed and continuous dynamical decoupling (DD) techniques enable the preservation of arbitrary states of the ensemble. These combined efforts could lead to the desired interaction-dominated regime. Finally, we simulate the effects of continuous and pulsed microwave (MW) control on the resulting NV-NV many body dynamics in a realistic spin-bath environment. We emphasize that dominant interaction sources could be identified and decoupled by the application of proper pulse sequences, and the modification of such sequences could lead to the creation engineered interaction Hamiltonians. Such interaction Hamiltonians could pave the way toward the creation of non-classical states, e.g. spin-squeezed states, which were not yet demonstrated in the solid-state, and could eventually lead to magnetic sensing beyond the standard quantum limit (SQL).

Levitated particles are attractive systems for precision optomechanics due to their extreme isolation from their environment. Here we describe several experiments with microparticles in magneto-gravitational traps, which use a combination of diamagnetism and the earth's gravity. First, the center-of-mass motion of the particle can be cooled to temperatures far below the ambient temperature using feedback. Second, the change in the frequency of oscillation of the particle under the influence of field masses can be used to measure the Newtonian gravitational constant. Finally, the fjrst steps towards producing and trapping silicon carbide microcrystals, which may contain optically-addressable defect centers, are reported.

Nano-NMR is an emerging field, striving to bring classic NMR techniques to a single molecule resolution. In recent years nitrogen vacancy centers, have been shown to be a promising experimental platform for that purpose. The main idea behind these experiments in liquids, is that the molecules create a time varying magnetic field at the NV's location, which causes the NV to dephase. The dephasing rate is related to the power spectrum of the magnetic noise, and thus encodes the NMR spectra. Understanding the diffusion spectrum is therefore key to future advancements in the field. In this work we calculate analytically the auto-correlation of the magnetic field at the NV's location. We then provide an asymptotic behavior of the power spectrum. These two results can be used to estimate the liquid's self-diffusion coefficient and the NV's distance from the diamond surface.

Fast-light phenomena can enhance the sensitivity of an optical gyroscope of a given size by several orders of magnitude, and could be applied to other optical sensors as well. MagiQ Technologies has been developing a compact fiber-based fast light Inertial Measurement Unit (IMU) using Stimulated Brillouin Scattering in optical fibers. We will report on our findings, including repeatable fast-light effects in the lab, numerical analysis of noise and stability given realistic optical specs, and methods for optimizing efficiency, size, and reliability with current technologies. The technology could benefit inertial navigation units, gyrocompasses, and stabilization platforms, and could allow high grade IMUs in spacecraft, unmanned aerial vehicles or sensors, where the current size and weight of precision gyros are prohibitive. By using commercially mature technologies, we believe that our design is appropriate for development without further advances in materials or components.

A new gyroscope architecture inspired by parity-time-symmetric optics is proposed and theoretically modeled. It consists of two ring resonators coupled together, one with loss and the other with gain, with a loss and gain selected such that the device does not lase. A narrow-linewidth laser is coupled into the loss ring to probe the coupled resonator’s rotation-dependent resonances, and a detector measures the rotation-induced change in the power transmitted by the device. Assuming that the small-signal gain is smaller than the loss, a common radius for the two rings of 5 cm, and imposing that the power in the gain medium never exceeds 10% of the saturation power to avoid gain saturation, we demonstrate that this structure has a sensitivity to rotation ~170 times larger than an optimized resonant fiber optic gyroscope of equal ring radius and loss. Such loss-gain coupled resonators are known to exhibit an exceptional point at a critical value of the coupling between resonators, at which point the device’s resonances become extremely sensitive to external perturbations such as a rotation. However, we demonstrate that the maximum rotation sensitivity of this paritytime- symmetric structure does not occur at the exceptional point. Instead, for the aforementioned parameter values and the imposition of a small circulating power, it is maximum when the inter-ring coupling is ~11% stronger than the exceptional-point coupling. This significant increase in rotation sensitivity is found to result to a much larger degree from a strong enhancement in the power circulating in the gain ring (although there is not a one-to-one correspondence), and to a much lower extent from an enhancement in the rotation-induced resonance-frequency shift.

We consider a PT-symmetric laser system comprising active and passive (lossy) coupled micro-resonators. It is shown that at its exceptional point (EP), the system satisfies the white light cavity (WLC) condition, exhibiting zero group index Slightly above lasing threshold, in the broken symmetry regime near the EP, the system exhibits “superluminal” lasing. It is also shown that some of the latest experimental studies involving PTSSs have indirectly demonstrated such superluminal lasing.

We theoretically study both the technical and the fundamental quantum limitations of the sensitivity of a resonant optical gyroscope based on a high finesse optical cavity. We show that the quantum back action associated with the resonantly enhanced optical cross and self-phase modulation results in the nonlinear optics-mediated standard quantum limit (SQL) of the angle random walk of the gyroscope. We also found that the measurement sensitivity of a generic optical gyroscope is fundamentally limited due to the opto-mechanical properties of the device. Ponderomotive action of the light interrogating the gyroscope cavity leads to the opto-mechanical SQL of the rotation angle detection. The uncorrelated quantum fluctuations of power of clockwise and counterclockwise light waves result in optical power-dependent uncertainty of the angular gyroscope position.

In this talk I explain that enhancement of performance of almost any optical device such as sensor modulator, amplifier or any nonlinear device in the end intimately connected to increasing the time of light-matter interaction, i.e. reducing the group velocity of light. Such similarly different phenomena as ENZ (epsilon near zero), plasmonics, micro-cavities and photonic crystals can all be characterized using the same slow light formalism.

Thanks to their transparency in a wide range of the electromagnetic spectrum and high birefringence, liquid crystals offer a versatile platform for light manipulation. Several optical functions, as spectral filters, light shaping, delay lines and phase shifter are implemented. Controlling group delay can be directly achieved for ultrafast (femtosecond) pulses by using simple nematic liquid crystal cells, offering potential applications in coherent beam combining and ultrafast optical measurement. On the other hand, by exploiting two-wave mixing in liquid crystal light-valves, a large group delay is produced in the liquid crystal layer. The large group delay induces an enhanced phase sensitivity, which can be exploited for precision interferometry and high sensitivity Doppler shift detection.

Noise is usually something that one would like to avoid when performing measurements. However, the information contained in fundamental noises might be of great interest for physicists. A recent example is the development of spin noise spectroscopy (SNS). In magnetic systems, the spectroscopy of the fundamental noise due to random spin fluctuations can be optically performed, by measuring the associated fluctuations of the Faraday rotation experienced by a linearly polarized probe beam, which propagates through the sample in the presence of a dc magnetic field [1]. Although a first experimental effort was initially reported in the early 1980s [2], only recently this method has seen a renewed interest due to advances in narrow line-width lasers and development in low noise electronics required for spectrum analysis [3]: it is now used to probe different properties of various media such as thermal atomic vapors, semi-conductors or quantum wells or defects in diamond [4]. In this talk, we will report our efforts to use this technique to probe the transitions of metastable helium and to understand the differences between the SNS spectra obtained along the different transitions. [1] V. S. Zapasskii, Adv. Opt. and Phot. 5 131 (2013) [2] E. B. Aleksandrov and V. S. Zapasskil, JETP 54 64 (1981) [3] S. A. Crooker, D. G. Rickel, A. V. Balatsky, and D. L. Smith, Nature 431 49 (2004) [4] N. A. Sinitsyn and Y. V. Pershin, Rep. on Prog. in Phys. 79 , 106501 (2016)

Quantum interface between photons is a long- standing goal of fundamental significance, and also serves as powerful tools for quantum technologies. Remarkable advances in quantum optics have recently developed in several platforms to demonstrate the generation of optical nonlinearities at the level of individual photons, which enable a number of unique applications such as light-by-light control at quantum level. Here, we present two examples in the realm of continuous variables based on the platform of flying atoms where thermal motion of atoms with long-lived coherence of ground state mediate the coupling between the spatially separated optical channels.

A speckle pattern denotes a random granular distribution of intensity generated, e.g., by light scattered from a disordered structure or transmitted through a multimode fiber. Its spectral sensitivity has been used to retrieve the spectrum of light that creates it. We have developed three types of speckle-based spectrometers. The first one is a chip-scale random spectrometer that enhances spectral sensitivity by multiple scattering of light. The second type utilizes a multimode optical fiber to achieve the record-high resolution. The third one is based on an evanescently-coupled multimode spiral waveguide. The speckle-based spectrometer has been applied to the ultrahigh-resolution frequency-comb spectroscopy.

Gravitational decoherence and gravitational wave function collapse are presented as two related but conceptually distinct ideas. Gravitational decoherence measures the effect of gravitational perturbations on the evolution of quantum systems, in particular their progressive lack of coherence. Gravitational wave function collapse starts with the assumption that the Schr¨odinger equation is not entirely right, and must be supplemented with extra terms, which cause the (random) collapse of the wave function; the collapse is then linked to gravity. Some of the most popular models are reviewed, with an emphasis on their conceptual status, stage of development, and open questions.

The sensitivity of coherent Raman spectroscopy methods such as Stimulated Raman Spectroscopy (SRS) or Coherent Anti-Stokes Raman Spectroscopy (CARS), is ultimately limited by shot noise from the stimulating fields. We present sub-shot-noise and background-free squeezed-light Raman spectroscopy, where the resonant Raman gain of the sample is enhanced by the quantum squeezing of two parametric amplifiers, while the nonresonant background of the Raman response in the sample is eliminated by destructive interference. Our configuration incorporates the Raman sample between two parametric amplifiers that squeeze the light in orthogonal quadrature axes (forming a nonlinear SU(1,1) interferometer), where the presence of a resonant Raman response induces a nonlinear phase shift, which can be measured below the shot-noise limit due to the squeezed illumination. Seeding the interferometer with coherent input further increases the Raman signal, similar to classical coherent methods. Thus, this method gains the benefits of both the coherent (classical) amplification of the seed and the squeezing-enhanced (quantum) sub-shot-noise sensitivity.

Two-wave mixing adaptive interferometers based on photorefractive crystals allow for precise remote detection of small displacements. Using dynamic holograms, they compensate for ambient disturbances in factory environments and can process speckled beams with complicated wavefronts. Linear phase-to-intensity conversion with maximum sensitivity is achieved when the response becomes local when a dc-field is applied to the photorefractive crystal. In the present work we study experimentally the change of the shape of the amplification spectrum induced by a dc field in the two-wave mixing geometry. The shape of the spectrum is used for identification of the type of response (local or nonlocal). High sensitivity for detection of surface displacements is demonstrated for a two-wave mixing interferometer with a dc-biased CdTe:Ge crystal.

Two-wave mixing adaptive interferometer based on photorefractive crystal allows for compensation of temporal disturbances in ambient environment and operation with speckled beams. The crystal should exhibit large effective trap density, low dark conductivity and large photoconductivity. Deliberately doped semiconductor may meet these requirements. In the present work the photorefractive, spectroscopic and magneto-optical study of CdTe:Sn is performed aiming to estimate these characteristics and to describe the space-charge formation. The photon energies for optical ionization/neutralization of the tin ions are estimated. The crystal is characterized as a medium for two-wave mixing adaptive interferometer with excellent performance.

As reported at Photonics West last year, diode pumped solid state (DPSS) green laser pointer modules (GLP) can have surprisingly good spectral characteristics and operate with a near single longitudinal-mode and narrow linewidths (approx. 30 kHz). Linewidths are measured by beat-notes against a kHz linewidth DPSS NPRO laser. Here we report that it is possible to phase-lock the optical frequency of the GLP to a self-referenced fs-optical-frequency-comb. This allows us to both know and control the absolute optical frequency of the GPL relative to a high-stability quartz-crystal oscillator that is steered to GPS signals. GPS and other GNSS signals are available everywhere and provide excellent frequency accuracy from the atomic clocks in space that are in turn steered by the elaborate world-wide GNSS infra-structure and ultimately referenced to high-accuracy primary atomic frequency standards. GPS-steered (disciplined) quartz crystal oscillators are readily available from many sources and provide a simple route to fractional frequency instability of about 1x10-12 for τ ≲ 1000 s and on longer time scales the frequency knowledge improves as roughly 1/ τ reaching the 10-14 range at 105 s. A fs-comb can transfer that stability and accuracy to the optical region with high fidelity. Characterization of GLP The DPSS GLP are particularly interesting and convenient. They provide excellent power (10’s of mW) at 532 nm and 1064 nm, with near-TEM00 spatial-mode. With some care in controlling operating conditions GLP can provide nearly signal-longitudinal-mode operation with a narrow-linewidth, and the optical frequency can be stabilized with simple control systems to iodine saturated-absorption signals or as described here GNSS-GPS frequency references. Typical modern GLP are based upon an 808 nm diode laser that pumps a short NdYVO4 gain chip that lases at 1064 nm and is directly bonded to a KTP crystal that doubles the frequency to 532 nm. However, the compact GLP also have some limitations, including: regions of operating parameters (temperature, pump-laser power and spectral characteristics) where the GLP operates on several modes (1 to > 5), regions that have significant instability and noisy (AM and FM). Some regions of the parameter space also show large relaxation oscillations at low frequencies (e.g. near 1 MHz). So far, we have not done a statistically significant study of the performance characteristics of the GLP. However, we find that the majority of the GLPs that we have tested have usefully large regions of temperature and pump-laser current where the GLP will run reliably on a dominant single longitudinal-mode for long periods of time (about two years is our longest test to date). Approach – GPS steering of visible lasers. The basic approach is: Received GPS signals steer the frequency of a high-stability quartz crystal oscillator that is used to lock the repetition rate (frep) and offset frequency (fceo) of the fs-comb. In our current experiments we use a commercial self-referenced fs-optical frequency comb centered at 1560 nm that is spectrally broadened in highly nonlinear (HNL) optical fiber to cover the spectral range from about 1000 nm to 2000nm. Beatnotes between the super-continuum from the fs-comb and the cw GLP are done at 1064 nm. To extract the 1064 nm from the GLP we removed the filter that blocks the 1064 nm output from the NdYVO4-KTP resonator. [Note: We find that in some low cost GLP significant (10’s of mW) 1064 nm already leaks out along with the 532 nm.] A beatnote between the 1064 nm output from the GLP and a mode of the broadened super-continuum from the fs-comb is then processed in a phase-frequency detector circuit to generate an error-signal that is used to control the optical frequency of the GLP. Course tuning of the GLP frequency is done with temperature combined with the DC set point of the injection current of the pump laser. Frequency stabilization is achieved via the pump-laser injection current, which changes the 808 nm pump-power and tunes the frequency of the NdYVO4 laser by changes in the gain and temperature within the lasing mode. For normal operating conditions, we measure an effective frequency response bandwidth (3 dB) of roughly1 kHz for pump laser control of the GLP optical frequency. Because the intrinsic frequency stability of the GLP is quite good (measured spectral linewidth ≈ 30 kHz) the frequency control via pump power is sufficient to achieve a phase-lock to the self-referenced fs-comb. The residual fractional frequency instability in the optical phase-lock is measured to be approximately 2 x10-14/ τ , for averaging time τ in seconds. This is well below the instability of even the most stable high quartz crystal oscillators, (in our case the quartz instability is slightly less than 1x10-12 for τ < 300s. On short time scales ≲ 100 ms the GLP has better stability and narrower linewidth than the modes of the super-continuum from the GPS steered self-referenced fs-comb. That is because the intrinsic stability of the GLP is better than the phase-noise of even a high-quality quartz crystal when multiplied up to 500 THz. The multiplication to optical frequencies produces comb-mode linewidths of about 300 kHz to 2 MHz. With our sincere thanks for the loan of a Si3N4 waveguide chip from NIST, we have also successfully detected good quality beatnotes at 1064 nm between the GLPs and the remarkable super-continuum that is generated by the Si3N4 waveguides. Those beatnotes have also been used to phase-lock the GLP and to detect fceo. However, currently our best performance comes from the supercontinuum from the HNL fiber. Nonetheless, given the very broad super-continuum that can be generated by Si3N4 waveguides it should be feasible to use GPS, as done here, to control the frequency of visible lasers with wavelengths ranging from 400 nm and 2000 Performance Results The net result of the approach reported here is GPS-steered GLP at 532 nm (563 THz) and 1064 nm (281 THz) that provides 10’s of mW of output power in the green and IR, with good spatial modes, dominantly single-longitudinal-mode, with a linewidth of ≈ 30 kHz, and center frequency stabilized to 500 Hz (σy(τ) ≤ 1x10-12 for averaging times ≳ 30 ms). The absolute frequency is known to 12 digits when locked to GPS. [We note that, at least in principle, the GLP could stay locked and steered to GPS for long durations, in which case commercial GPS-steered quartz oscillators can provide long-term frequency stability that averages down into the 10-14 range, (corresponding to 5 Hz at 500 THz)]. Achieving optical phase-lock ensures that the 563 THz (532 nm) frequency is stabilized relative to the GPS reference, but, as usual, to know the absolute optical frequency requires determination of the large integer N of the fs-optical comb mode (comb mode frequency fN = Nfrep + fceo ). In our case, the pulse repetition frequency frep= 250 MHz and the carrier envelope offset frequency fceo=20 MHz). N can be determined by measuring the cw laser wavelength/frequency using a wavemeter that has six digits of accuracy, or by keeping the cw laser stable and changing frep sufficiently to determine N, or in many cases of interest in AMO science, atomic/molecular spectra can provide sufficient knowledge of N. In the case of GLP it is sometime feasible to use molecular iodine spectra to determine N. The frequency instability and frequency accuracy of the GPS-steered-quartz and subsequently the locked fs-comb are verified in our lab by independent and long-term measurements against Cs and Rb atomic frequency standards, and also previously against Sr-optical and H-maser frequency references. GLPs provide convenient, bright green 532 nm, and 1064 nm near IR, and if frequency stabilized can serve as optical frequency and wavelength references for numerous applications. When steered to GPS these lasers can provides 12 digits of frequency accuracy and a short-term spectral linewidth of about 30 kHz. That performance exceeds the requirements of most real-world applications of frequency-stabilized lasers (e.g. calibration of spectrometers, references for interferometers, dimensional metrology, coordinate measuring and position control systems, references for atomic and molecular spectroscopy, etc.). With increasing availability and simplification of fiber-based mode-locked lasers that can be “self-referenced” the approach outlined here becomes an attractive method for absolute frequency stabilization of multiple laser frequencies that are typical used in atomic physics and cold-atom experiments (e.g. in our lab for Yb, I2, Rb, Cs, etc.) Acknowledgments. This research was supported in-part by the DARPA-ACES program. We also thank A. Cable, D. Carlson, and S. Papp for important contributions to this project. References i) e.g. green laser pointer module, https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=5597 ii) Websites of: MicroSemi, FEI-/Zyfer, Stanford Research, EndRun Technologies, etc. iii ) Menlo Systems, Er-fiber based fs comb.

Quantum metrology has many important applications in science and technology, ranging from frequency spectroscopy to gravitational wave detection. Quantum mechanics imposes a fundamental limit on measurement precision, called the Heisenberg limit, which can be achieved for noiseless quantum systems, but is not achievable in general for systems subject to noise. Here we study how measurement precision can be enhanced through quantum error correction, a general method for protecting a quantum system from the damaging effects of noise. We find a necessary and sufficient condition for achieving the Heisenberg limit using quantum probes subject to Markovian noise, assuming that noiseless ancilla systems are available, and that fast, accurate quantum processing can be performed. When the sufficient condition is satisfied, the quantum error-correcting code achieving the best possible precision can be found by solving a semidefinite program. We also show that noiseless ancilla are not needed when the signal Hamiltonian and the error operators commute. Finally we provide two explicit, archetypal examples of quantum sensors: qubits undergoing dephasing and a lossy bosonic mode.

We will present our current efforts on single photon quantum metrology using high-efficiency superconducting detectors and high-efficiency single-photon sources based on spontaneous parametric downconversion. Optical power measurements based on single photon counting could establish a quantum standard for optical power calibration in the future. At NIST we are pursuing the development of single photon sources and single photon detectors for metrology, quantum and classical applications. As part of these efforts, we are pursuing the establishment of a measurement service for the calibration of single photon detectors. We present how our calibration is tied to the calibration of our transfer standard optical fiber power meters. Using the beamsplitter method, we have implemented a fiber-coupled and free-space measurement system. Also, we have developed testbeds and measurement protocols for the characterization of single photon sources and single photon detectors. We will review several methods, which allow for the characterization of the spatial and spectral degree of freedom in spontaneous parametric downconversion.

The control of photons represents a pillar for our modern technological society. The emerging field of quantum photonics exploits quantum properties of light to dramatically improve the performance of protocols for metrology, communication and information processing. However, modern applications exploit very little of the enormous potential of the photon. Unfortunately, the challenges involved in the preparation and characterization of photonic states with multiple particles, impose practical limitations to realistic quantum technologies. In this talk, I will report on our recent results on the preparation, manipulation and characterization of quantum states with multiple photons. I will describe how the manipulation of the quantum electromagnetic fluctuations of a pair of vacuum states leads to a novel family of quantum-correlated multiphoton states with tunable mean photon numbers and degrees of correlations. Our technique relies on the use of conditional measurements to engineer the vacuum and consequently the excitation mode of the field through the simultaneous subtraction of photons from two-mode squeezed vacuum states. In addition, I will describe the potential of combing these states with photon number resolving measurements for quantum phase estimation. The last part of my talk will be devoted to discuss our recent technique that allowed us to utilize compressive sensing to demonstrate measurement of high-dimensional states, that describe telecom photon pairs in the spatial and spectral degrees of freedom, with 12 billions of elements using only a small fraction of measurements.

In this paper we describe the preliminary results obtained at INRiM laboratories toward realizing a couple of correlated power-recycled Michelson interferometers. This system is the first step toward the realization of a quantum-enhanced holometer.

We consider the role of detection noise in quantum-enhanced metrology in collective spin systems, and derive a fundamental bound for the maximum obtainable sensitivity for a given level of added detection noise. We then present an interaction-based readout utilising the commonly used one-axis twisting scheme that approaches this bound for states generated via several commonly considered methods of generating quantum enhancement, such as one-axis twisting, two-axis counter-twisting, twist-and-turn squeezing, quantum non-demolition measurements, and adiabatically scanning through a quantum phase transition. We demonstrate that this method performs significantly better than other recently proposed interaction-based readouts. These results may help provide improved sensitivity for quantum sensing devices in the presence of unavoidable detection noise.

We discuss the relationship between quantum coherence of finite dimensional systems and nonclassical quantum light. We demonstrate that quantifying the quantum coherence between coherent states always leads to a quantifier of nonclassicality that monotonically decreases under linear optical operations. This allows us to introduce a resource theory of nonclassicality based on linear optics that closely parallels the resource theory of coherence. Finally, we discuss the metrological power of a quantum state, which quantifies how sensitive a quantum state is to displacement operations. It is then shown that the metrological power leads to a nonclassicality monotone.

Technological advancements in the creation, manipulation and detection of quantum states of light have motivated the application of such states to overcome classical limits in sensing and imaging. In particular, there has been a surge of recent interest in super-resolution imaging based on principles of quantum optics. However, the application of such schemes for practical imaging of biological samples is demanding in terms of signal-to-noise ratio, speed of acquisition and robustness with respect to sample labeling. Here, we re-introduce the concept of quantum image scanning microscopy (Q-ISM), a super-resolution method that enhances the classical image scanning microscopy (ISM) method by measuring photon correlations. Q-ISM was already utilized to achieve super-resolved images of a biological sample labeled with fluorescent nanoscrystals whose contrast is based entirely on a quantum optical phenomenon, photon antibunching. We present here an experimental demonstration of the method and discuss with further details its prospects for application in life science microscopy.

The precision in phase measurement is determined by the number of resources that are used. The minimum uncertainty that can be achieved with uncorrelated resources is the shot-noise limit (SNL), while the ultimate precision limit set by quantum mechanics is the Heisenberg limit (HL). First, we will discuss the task of phase sensing, which deals with determining small deviations in a phase about an already known value. Despite theoretical proposals stretching back decades, no measurement using photonic (i.e. definite photon number) states has unconditionally surpassed the SNL in phase sensing. Previous demonstrations employed postselection to discount photon loss in the source, interferometer or detectors. In our demonstration we used the state-of-art single photon generation and detection technology to respectively make and measure a two-photon NOON state and use it to perform unconditional phase sensing beyond the SNL — that is, without artificially correcting for loss or any other source of imperfection. Next, we present an experimental demonstration of a new protocol for the ab-initio phase estimation, where the goal is to measure a completely unknown optical phase. Until now, and despite intense theoretical attention, no technique has been proposed or implemented for such a measurement with ultimate precision, at the exact HL. Our measurement protocol combines several approaches, such as entanglement, multiple applications of the phase shift and simulated adaptive measurement. With it we experimentally realized the optimal phase measurement scheme for three resources, achieving a precision within 4% of the exact HL (postselected on detected coincidence counts, in this case).

How can quantum mechanics deliver better imaging performance? Parametric down-conversion sources produce pairs of photons that are correlated in many degrees of freedom, including their spatial positions. By using a camera to detect these pairs of photons it is possible configure imaging systems that can either beat the classical resolution limit or the classical noise limit. We demonstrate how a simple down-conversion source based on a laser and non-linear crystal can be combined with an EMCCD camera to achieve either of these outcomes. Firstly, when both photons pass through the sample, we show a full-field, resolution-enhancing scheme, based on the centroid estimation of the photon pairs. By optimising the software control of the EMCCD camera running in the photon-sparse regime we achieve a resolution enhancement over the equivalent classical limit. Secondly, we show a similar scheme but where only one of the two photons pass through the sample and the other acts as a reference, in this case the ratio of the two resulting images eliminates the background noise of the camera, and background light, achieving an increase in image contrast.

Imaging with non-classical photons allows to bypass the Rayleigh resolution limit and classical shot-noise level. One step towards imaging demonstration with large photon numbers is the separation of non-classical photon states from the classical photons, thus increasing dynamic range and signal to background contrast on the detector. We demonstrate the feasibility of such separation by an échelle grating at high diffraction orders. In our demonstration, a PPKTP crystal generates entangled photon pairs in type-0 SPDC. The crystal is cw pumped and produces non-collinear degenerated photon pairs at 810nm. The classical light states are produced by a VCSEL at nearly same wavelength. After diffraction on echelle grating, the spatial far-field patterns and the photon arrival times are recorded by a novel 32×32 SPAD array sensor with 160 ps timing resolution. It allows real-time monitoring of the first- and second order correlation patterns. Within the observation window, we detected correlated biphoton arrivals in the four diffraction orders corresponding to their de Broglie wavelength, which is a half of the classical wavelength. Respectively a half of these diffraction orders is prohibited for classical photons. Placing a slit mask in these orders allows us to transmit only non-classical photon state and block the classical ones. We report on a series of experiments elucidating spatial and temporal correlations at the output of such quantum –classical photon discriminator. Those results could be used for the separation of biphotons from classical photons at the same wavelength in high-intensity light sources.

Abstract Not Submitted

We describe an implementation of a Sagnac interferometer using a Bose-Einstein condensate confined in a harmonic time-orbiting potential trap. Atoms are manipulated using Bragg laser beams to produce two reciprocal interferometers, providing common-mode rejection of accelerations, trap fluctuations, and most other effects. The Sagnac rotation phase is differential. The orbit of the atoms is nearly circular, with an effective Sagnac area of about 0.5 mm².

Over the past few decades, the development of laser-cooling techniques has made it possible to exploit the quantum properties of matter at very low temperatures. These techniques have enabled experimentalists to coherently manipulate quantum objects with a very high degree of precision. In this context, atom interferometry has emerged as a powerful tool for metrology. Nowadays, atom interferometers (AIs) are used for a wide range of applications, such as sensitive probes of inertial forces, or studies of fundamental physics and tests of gravitational theories. Our experiment uses a dual-species gravimeter to test the weak equivalence principle (WEP). Here, two overlapped samples of 39K and 87Rb are simultaneously interrogated during free-fall—yielding a precise measurement of their differential acceleration under gravity. These experiments have been carried out in the weightless on ground and in the environment of parabolic flight. The new compact transportable quantum sensors used for drift-free integration in the 0-g airbus. The starting point for many experiments aimed at studying fundamental physics is to prepare a pure sample in terms of its energy, spin and momentum before injecting into an atom interferometer, spectrometer or quantum simulator. We will present an all-optical technique to prepare ultra-cold sample in magnetically insensitive state with high purity, a versatile preparation scheme particularly well suited to performing matter-wave interferometry with species exhibiting closely separated hyperfine levels, such as the isotopes of lithium and potassium. We will also present the recent progress in measuring the Eotvos parameter which compared the gravitational acceleration measured by two atomic species. We will finally discuss how precision atom interferometry can be used to perform long-term, drift-free integration even in the harsh environment of the plane, and thus provide a new tool for precision measurement and navigation.

Light-pulse atom interferometry—which uses optical pulses to split, recombine, and interfere quantum mechanical atomic matter waves—is a sensitive method for measuring inertial forces, making it a valuable tool for a broad set of applications and fundamental physics tests. The sensitivity of an atom interferometer scales with its enclosed spacetime area, which is proportional to the product of the maximum spatial separation reached between the two interferometer paths and the interferometer duration. Motivated by this scaling, we have realized atom interferometers that cover macroscopic scales in space (tens of centimeters) and in time (multiple seconds). I will present experimental results from the implementation of these large area interferometers as high-precision gravitational sensors. Subsequently, I will discuss a new experimental effort to use such gravitational sensors to look for new particles beyond the standard model, including light moduli associated with the compactified extra dimensions that arise in string theory, by searching for deviations from the gravitational inverse square law with improved sensitivity at the length scale of 10 cm to 1 m. This experiment could also provide a new measurement of Newton’s gravitational constant. In addition, large area atom interferometers using atom optics based on single-photon transitions on the clock transition of strontium have the potential to be excellent gravitational wave detectors in the frequency band from 300 mHz to 3 Hz, which is intermediate between the LIGO detector and the planned LISA detector. I will describe ongoing technology development efforts for an atomic gravitational wave detector.

Measurements of the fine-structure constant α require methods from across subfields and are thus powerful tests of the consistency of theory and experiment in physics. Using the recoil frequency of cesium-133 atoms in a matter-wave interferometer, we recorded the most accurate measurement of the fine-structure constant to date: α = 1/137.035999046(27) at 2.0 × 10^−10 accuracy. Using multiphoton interactions (Bragg diffraction and Bloch oscillations), we demonstrate the largest phase (12 million radians) of any Ramsey-Bordé interferometer and control systematic effects at a level of 0.12 part per billion. Comparison with Penning trap measurements of the electron gyromagnetic anomaly ge − 2 via the Standard Model of particle physics is now limited by the uncertainty in ge − 2; a 2.5σ tension rejects dark photons as the reason for the unexplained part of the muon’s magnetic moment at a 99% confidence level. Implications for dark-sector candidates and electron substructure may be a sign of physics beyond the Standard Model that warrants further investigation.

Emerging quantum materials are becoming the building blocks for quantum devices and they are enabling new advances from spintronics to topological insulators. Their functionality typically comes from their inner magnetic field structure. Neutrons are a particularly good probe to characterize such features. The control of neutron orbital angular momentum and the spin-orbit interaction enables new characterizing techniques and increased sensitivity towards specific material properties. Here we review the preparation and characterization methods of structured neutron waves.

We extend techniques commonly used in optical atomic clocks to perform precise metrology of binding energies and coherent control of deeply bound Sr2 molecules. Clock transitions between two vibrational levels in the electronic ground state potential are driven via two-photon Raman process. We achieve Rabi oscillations across the ground state potential and employ a magic wavelength technique to eliminate the differential light shift using narrow polarizability resonances. This allows us to increase coherence by three orders of magnitude and obtain a preliminary linewidth of <100 Hz for a 26 THz transition. This development clears the path toward the realization of a molecular clock for the study of fundamental physics.

We will describe a next-generation active atomic frequency reference based on super-radiant pulses of laser light from the ultra-narrow, 1 mHz linewidth, optical clock transition in an ensemble of cold ⁸⁷Sr atoms. Light is stimulated from the millihertz linewidth transition by confining an ensemble of laser cooled atoms inside of a high finesse optical cavity. Such a light source has been proposed as a next-generation active atomic frequency reference, with the potential to enable high-precision optical frequency references to be used outside laboratory environments. We achieve a remarkable short term fractional frequency stability, 6.7 × 10¹⁶ at 1 s of averaging, absolute accuracy, 2 Hz (4 × 10¹⁵ fractional frequency), and high insensitivity to changes in the cavity length that limits the performance of todays more stable lasers. We will also discuss current work on cavity-enhanced dispersive measurements to perform high resolution spectroscopy and atom counting.

We will present plans for a multiplexed optical lattice clock, and will discuss progress made towards its completion. This apparatus will allow for independent loading, preparation, and interrogation of two ensembles of strontium atoms in spatially separated, movable optical lattices. Simultaneous differential measurements of the two ensembles will offer common mode noise rejection of shared environmental perturbations and clock laser noise. We will propose new tests of relativity and methods for evaluating clock systematics using differential measurements, and discuss applications of a multiplexed optical lattice clock to gravitational wave detection and searches for beyond standard model physics.

The combination of coherent population trapping (CPT) and laser cooled atoms is a promising platform for realizing the next generation of compact atomic frequency references. Towards this goal, we have developed an apparatus based on the grating magneto-optical trap (GMOT) and the high-contrast lin ⊥ lin CPT scheme in order to explore the performance that can be achieved. One important trade-off for cold-atom systems arises from the need to simultaneously maximize the number of cold atoms available for interrogation and the repetition rate of the system. This compromise can be mitigated by recapturing cold atoms from cycle to cycle. Here, we report a quantitative characterization of the cold atom number in the recapture regime for our system, which will enable us to optimize this trade-off. We also report recent measurements of the short-term frequency stability with a short-term Allan deviation of 3 × 10^-11/τ up to an averaging time of τ = 10 s.

This paper presents an overview of technologies of MEMS Cs microcells for CPT-based atomic clocks, obtained in FEMTO-ST Institute over the last decade. We discuss the challenges in microfabrication of miniature cells: the different configurations of cells, two methods for filling alkali vapor cells with Cs from a dispenser pill and from the dispensing paste, and a study on the permeability of our microcells to the buffer gas limiting the sealing performances. Finally, we report on the aging tests and resulting short-term and long-term clock stability measurements.

Quantum technologies have been identified as breakthrough technologies with a potential high impact on future navigation, sensing and communication systems since the end of the 90’s. In this paper we will review how these technologies can contribute to electromagnetic spectrum dominance through the use of SHB (spectral hole burning) based spectral holography and of NV (nitrogen vacancy) centers in diamond. Quantum technologies, combined with integration techniques, will also improve the performances of navigation systems thanks to ultra-precise compacts atomic clocks, accelerometers and gyros.

Abstract Not Submitted

Correlated light (either classical or quantum) can be employed in various ways to improve resolution and measurement sensitivity. In an “interaction-free” measurement, a single photon can be used to reveal the presence of an object placed within one arm of an interferometer without being absorbed by it. This method has previously been applied to imaging. With a technique known as “ghost imaging”, entangled photon pairs are used for detecting an opaque object with significantly improved signal-to-noise ratio while preventing over-illumination. Here, we integrate these two methods to obtain a new imaging technique which we term “interaction-free ghost-imaging” that possesses the benefits of both techniques. While improving the image quality of conventional ghost-imaging, this new technique is also sensitive to phase and polarization changes in the photons introduced by a structured object. Furthermore, thanks to the “interaction-free” nature of this new technique, it is possible to reduce the number of photons required to produce a clear image of the object (which could be otherwise damaged by the photons) making this technique superior for probing light-sensitive materials and eventually biological tissues. If time allows, I will discuss some follow-up works involving partial measurements and remote erasure/completion of images. The latter techniques can help to suppress various types of noise during the imaging process.

Quantum Metrology calculates the ultimate precision of all estimation strategies, measuring what is their root mean-square error (RMSE) and their Fisher information. Here, instead, we ask how many bits of the parameter we can recover, namely we derive an information-theoretic quantum metrology. In this setting we redefine ``Heisenberg bound'' and ``standar quantum limit'' (the usual benchmarks in quantum estimation theory), and show that the former can be attained only by sequential strategies or parallel strategies that employ entanglement among probes, whereas parallel-separable strategies are limited by the latter. We highlight the differences between this setting and the RMSE-based one. This is joint work with Majid Hassani and with Chiara Macchiavello. It has been published in the paper: M. Hassani, C. Macchiavello, L. Maccone,``Digital quantum metrology'', Phys. Rev. Lett. 119, 200502 (2017).

see above

Recent advances in the level of precision in controlling atomic and optical systems have enabled the routine generation of quantum entanglement for sensing and information processing applications. In this talk I will focus on some properties, generation and usage of a particular set of entangled states called spin squeezed states, with an emphasis on recent experiments for characterizing the effects of atom loss and homogeneity loss.

In a conventional atomic interferometer employing N atoms, the phase sensitivity is at the standard quantum limit: 1/√N. Using spin-squeezing, the sensitivity can be increased, either by lowering the quantum noise or via phase amplification, or a combination thereof. Here, we show how to increase the sensitivity, to the Heisenberg limit of 1/N, while increasing the quantum noise by √N, thereby suppressing by the same factor the effect of excess noise. The proposed protocol makes use of a Schroedinger Cat (SC) state representing a mesoscopic superposition of two collective states of N atoms, behaving as a single entity with an N-fold increase in Compton frequency. The resulting N-fold phase magnification is revealed by using atomic state detection instead of collective state detection

We analyze the dynamics of spin-mixing interactions generated by coupling spin-1 atoms to the mode of a high-finesse optical cavity. We show that the dynamics can be understood in terms of generators of the noncompact Lie group SU(1, 1) and introduce a set of SU(1, 1) coherent states which are preserved under Hamiltonian evolution. In terms of these coherent states the resulting dynamics may be interpreted as classical motion on the unit disk. We explicitly compute the trajectories of this classical motion and show that the motion is equivalent to spin-nematic squeezing in the atomic ensemble. Non-uniform coupling between the atomic ensemble and the cavity mode leads to departures from this simple behavior; we introduce a toy model that captures this non-uniformity and solve it exactly.

Single organic dye molecules have been studied for almost three decades. A majority of experiments are now conducted under ambient conditions and aim towards material science and micro-biology. The experiments under cryogenic conditions are often based on highly rigid polycyclic hydrocarbons, which have excellent fluorescing properties when they are operated at temperatures below 2 K. Their photonic advantages integrate their high flux, their narrow-band nature and their tunability over the entire visible spectrum. Therefore the use of organic molecules as efficient and narrow-band single photon sources facilitated a number of quantum optical advances in the past years. The results mostly cover quantum sensing, the formation of quantum hybrid systems and the optical combination of multiple photons in all-optical experiments. Here we present all three fields and outline our own experiments in the combination of single molecule studies, atomic spectroscopy and entanglement generation. The brightness and the narrow-band nature of the molecules are outlined and a delayed-choice quantum eraser is presented. The mode-mixing of two photons on a beam-splitter allows for the generation of a degenerate photon pair, which is resonant to the sodium D₂-line. Furthermore, its spectral width matches roughly to the natural linewidth of an isolated sodium atom, such that further experiments are feasible. The entanglement of the post-selected photon pair is testified by a violation of Bell's inequality. Even the raw collected clicks violate Bell's inequality by more than two standard deviations.

Quantum-enhanced measurements represent the path towards the best measurement precision allowed by the laws of quantum mechanics. Known protocols usually rely on the preparation of entangled states and promise high or even optimal precision, but fall short in real-word applications because of the difficulty to generate entangled states and to protect them against decoherence. Here, we refrain from the preparation of entangled states but supplement the integrable parameter-encoding dynamics by non-linear kicks driving the system in the dynamical regime of quantum chaos. We show that large improvements in measurement precision are possible by modeling a spin-exchange relaxation-free alkali-vapor magnetometer where the non-linear kicks are realized by exploiting the ac Stark effect.

In this work, we present a family of direct tomography protocols that can characterize various types of high-dimensional photon states. In specific, we show direct tomography approaches that can measure high-dimensional spatial modes, spatial vector modes and partially-coherent modes. In direct tomography methods, the measurement readouts directly correspond to the complex-valued state vector or other quantities that describe the quantum system to be measured, and therefore can significantly reduce the complexity of tomography procedures for high-dimensional states. Moreover, we show that it is possible to design the tomography protocol such that all the information needed to describe the photon states can be acquired in a single experimental setup without any need of scanning. This is particularly interesting for real-time metrology of both quantum and classical photon states. The unique single-shot, direct characterization capability provide powerful real-time metrology tools that can boost fundamental studies and applications of high-dimensional photon states.

We generate quantum-correlated twin beams in a four-wave mixing process and study the mutual information after passing one of the beams through a phase-sensitive amplifier (PSA). It is found that the condition of noiseless amplification or deamplification by the PSA, where information is not degraded, coincides with the lack of any dispersion-like advance or delay of the signal.

Quantum teleportation means to transfer an unknown quantum state from one station to another over certain distance with the help of nonlocal Einstein-Podolsky-Rosen entangled state shared by sender and receiver. Here, we experimentally realize deterministic quantum teleportation of an optical coherent state through 6.0 kilometer fiber fiber-channel. The fidelity of 0.62±0.03 is achieved for the retrieved quantum state, which breaks through the classical limit of 1/2. A fidelity of 0.69±0.03 breaking through the no-cloning limit of 2/3 has also been achieved when the transmission distance is 2.0 kilometers. Our work provides a feasible scheme to implement deterministic quantum teleportation in communication networks.

Counterfactual communication, transferring bits and even qubits without particle travelling in the transmission channel is a bizarre quantum effect. It is also a very controversial topic. Here I will try to clarify the meaning of various “counterfactual" quantum protocols.

Atoms are extremely accurate resonators. This property serves to build up precise sensors for time keeping, accelerometer and many others. However, their accuracy depend on their environment. For example, at the vicinity of a surface (metallic or dielectric) the atomic resonances are shifted by the Casimir-Polder interaction. The spatial dependency of this interaction (1/z3, in the non retarded regime) can be a crucial limitation for the development of compact sensors at the micrometer size scale. To address this issue, we explore the tunability property of the Casimir- Polder interaction with resonant surface plasmon modes. These latter are generated using nano-structured metallic layers. We found that the atomic resonance shift can be almost suppressed and the Purcell factor enhanced. More recently, we investigate quadrupole atomic transitions in surface plasmon. Those transitions are extremely weak in vacuum (~1 Hz) but can be enhanced if the spatial variation of the electromagnetic field become stronger as expected with localized surface plasmons. In this context, we will present our results, obtained with a cesium vapor, and discuss the potential application of creating new excitation channels in atomic spectrum.