We perform generalized measurements of a qubit by realizing the qubit as a coin in a photonic quantum walk and subjecting the walker to projective measurements. Our experimental technique can be used to realize, photo...
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We perform generalized measurements of a qubit by realizing the qubit as a coin in a photonic quantum walk and subjecting the walker to projective measurements. Our experimental technique can be used to realize, photonically, any rank-1 single-qubit positive-operator-valued measure via constructing an appropriate interferometric quantum-walk network and then projectively measuring the walker’s position at the final step.
We develop a theory and accompanying mathematical model for quantum communication via any number of intermediate entanglement-swapping operations and solve numerically for up to three intermediate entanglement-swappin...
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We develop a theory and accompanying mathematical model for quantum communication via any number of intermediate entanglement-swapping operations and solve numerically for up to three intermediate entanglement-swapping operations. Our model yields two-photon interference visibilities postselected on photon counts at the intermediate entanglement-swapping stations. Realistic experimental conditions are accommodated through the parametric down-conversion rate, photon-counter efficiencies and dark-count rates, and instrument and transmission losses. We calculate achievable quantum communication distances such that two-photon interference visibility exceeds the Bell-inequality threshold.
We study phase-sensitive amplification of electromagnetically induced transparency in a warm Rb85 vapor wherein a microwave driving field couples the two lower-energy states of a Λ energy-level system thereby transfo...
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We study phase-sensitive amplification of electromagnetically induced transparency in a warm Rb85 vapor wherein a microwave driving field couples the two lower-energy states of a Λ energy-level system thereby transforming into a Δ system. Our theoretical description includes effects of ground-state coherence decay and temperature effects. In particular, we demonstrate that driving-field-enhanced electromagnetically induced transparency is robust against significant loss of coherence between ground states. We also show that for specific field intensities, a threshold rate of ground-state coherence decay exists at every temperature. This threshold separates the probe-transmittance behavior into two regimes: probe amplification vs probe attenuation. Thus, electromagnetically induced transparency plus amplification is possible at any temperature in a Δ system.
The NOON state, which was introduced as a resource for quantum-enhanced metrology, is in fact a special case of a superposition of two SU(2) coherent states. Here we show explicitly the derivation of the NOON state fr...
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The NOON state, which was introduced as a resource for quantum-enhanced metrology, is in fact a special case of a superposition of two SU(2) coherent states. Here we show explicitly the derivation of the NOON state from the superposition state. This derivation makes clear the connection between these seemingly disparate states and shows how the NOON state can be generalized to a superposition of SU(2) coherent states.
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