4,737 research outputs found
Effects of depolarizing quantum channels on BB84 and SARG04 quantum cryptography protocols
We report experimental studies on the effect of the depolarizing quantum
channel on weak-pulse BB84 and SARG04 quantum cryptography. The experimental
results show that, in real world conditions in which channel depolarization
cannot be ignored, BB84 should perform better than SARG04.Comment: 4 pages, 4 figure
Single-photon quantum nonlocality: Violation of the Clauser-Horne-Shimony-Holt inequality using feasible measurement setups
We investigate quantum nonlocality of a single-photon entangled state under
feasible measurement techniques consisting of on-off and homodyne detections
along with unitary operations of displacement and squeezing. We test for a
potential violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality, in
which each of the bipartite party has a freedom to choose between 2 measurement
settings, each measurement yielding a binary outcome. We find that
single-photon quantum nonlocality can be detected when two or less of the 4
total measurements are carried out by homodyne detection. The largest violation
of the CHSH inequality is obtained when all four measurements are
squeezed-and-displaced on-off detections. We test robustness of violations
against imperfections in on-off detectors and single-photon sources, finding
that the squeezed-and-displaced measurement schemes perform better than the
displacement-only measurement schemes.Comment: 7+ pages, 7 figures, 1 table, close to published versio
Experimental verification of the commutation relation for Pauli spin operators using single-photon quantum interference
We report experimental verification of the commutation relation for Pauli
spin operators using quantum interference of the single-photon polarization
state. By superposing the quantum operations and on a single-photon polarization state, we have experimentally
implemented the commutator, , and the anticommutator,
, and have demonstrated the relative phase factor
of between and operations. The
experimental quantum operation corresponding to the commutator, , showed process fidelity of 0.94 compared to the ideal
operation and is determined to be .Comment: 4pages, 3 figure
Reversing the Weak Quantum Measurement for a Photonic Qubit
We demonstrate the conditional reversal of a weak (partial-collapse) quantum
measurement on a photonic qubit. The weak quantum measurement causes a
nonunitary transformation of a qubit which is subsequently reversed to the
original state after a successful reversing operation. Both the weak
measurement and the reversal operation are implemented linear optically. The
state recovery fidelity, determined by quantum process tomography, is shown to
be over 94% for partial-collapse strength up to 0.9. We also experimentally
study information gain due to the weak measurement and discuss the role of the
reversing operation as an information erasure
Two-photon interference with continuous-wave multi-mode coherent light
We report two-photon interference with continuous-wave multi-mode coherent
light. We show that the two-photon interference, in terms of the detection time
difference, reveals two-photon beating fringes with the visibility .
While scanning the optical delay of the interferometer, Hong-Ou-Mandel dips or
peaks are measured depending on the chosen detection time difference. The HOM
dips/peaks are repeated when the optical delay and the first-order coherence
revival period of the multi-mode coherent light are the same.Comment: 9 pages, 5 figure
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