Decoherence, which causes degradation of entanglement and in some cases entanglement sudden death, is a critical issue faced in quantum information. Protecting entanglement from decoherence, therefore, is essential in practical realization of quantum computing and quantum communication protocols. In this paper, we demonstrate a novel method to protect entanglement from amplitude damping decoherence via weak measurement and quantum measurement reversal. It is shown that even entanglement sudden death can be circumvented.
The partial transpose by which a subsystem's quantum state is solely transposed is of unique importance in quantum information processing from both fundamental and practical point of view. In this work, we present a practical scheme to realize a physical approximation to the partial transpose using local measurements on individual quantum systems and classical communication. We then report its linear optical realization and show that the scheme works with no dependence on local basis of given quantum states. A proof-of-principle demonstration of entanglement detection using the physical approximation of the partial transpose is also reported.
The partial transpose by which a subsystem's quantum state is solely transposed is of unique importance in
quantum information processing from both fundamental and practical point of view. In this work, we present a
practical scheme to realize a physical approximation to the partial transpose using local measurements on individual
quantum systems and classical communication. We then report its linear optical realization and show that
the scheme works with no dependence on local basis of given quantum states. A proof-of-principle demonstration
of entanglement detection using the physical approximation of the partial transpose is also reported.
Spatial interference of quantum mechanical particles exhibits a fundamental feature of quantum mechanics. A
two-mode entangled state of N particles known as N00N state can give rise to non-classical interference. We
report the first experimental observation of a three-photon N00N state exhibiting Young's double-slit type spatial
quantum interference. Compared to a single-photon state, the three-photon entangled state generates interference
fringes that are three times denser. Moreover, its interference visibility of 0.49 ± 0.09 is well above the limit of
0.1 for spatial super-resolution of classical origin. The demonstration of spatial quantum interference by a N00N
state composed of more than two photons represents an important step towards applying quantum entanglement
to technologies such as lithography and imaging.
The universal transpose of quantum states is an anti-unitary transformation that is not allowed in quantum
theory. In this work, we investigate approximating the universal transpose of quantum states of two-level
systems (qubits) using the method known as structural physical approximation. We also report its experimental
implementation in linear optics. The scheme is optimal in that the maximal fidelity is attained, and also practical
as measurement and preparation of quantum states that are experimentally feasible within current technologies
are solely applied.
The universal transpose of quantum states is an anti-unitary transformation that is not allowed in quantum
theory. In this work, we investigate approximating the universal transpose of quantum states of two-level
systems (qubits) using the method known as structural physical approximation. We also report its experimental
implementation in linear optics. The scheme is optimal in that the maximal fidelity is attained, and also practical
as measurement and preparation of quantum states that are experimentally feasible within current technologies
are solely applied.
We have studied experimentally the effect of a depolarizing quantum channel on polarization-encode weak pulse
BB84 and SARG04 quantum cryptography. Experimental results show that, in real world conditions in which
channel depolarization cannot be ignored, BB84 is more robust than SARG04 on the effect of the depolarizing
quantum channel.
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