All-linear-optical scheme for fully featured quantum router is presented.
This device directs the signal photonic qubit according to the state of one
control photonic qubit. In the introduction we formulate the list of
requirements imposed on a fully quantum router. Then we describe our proposal
showing the exact principle of operation on a linear-optical scheme.
Subsequently we provide generalization of the scheme in order to optimize the
success probability by means of a tunable controlled-phase gate. At the end, we
show how one can modify the device to route multiple signal qubits using the
same control qubit.Comment: 7 pages, 6 figure
We propose a linear-optical scheme for an efficient amplification of a photonic qubit based on interaction of the signal mode with a pair of entangled ancillae. In contrast to a previous proposal for qubit amplifier by Gisin et al., [Phys Rev. Lett. 105, 070501 (2010)] the success probability of our device does not decrease asymptotically to zero with increasing gain. Moreover we show how the device can be used to restore entanglement deteriorated by transmission over a lossy channel and calculate the secure key rate for device-independent quantum key distribution.
We report on the first experimental realization of optimal linear-optical controlled phase gates for arbitrary phases. The realized scheme is entirely flexible in that the phase shift can be tuned to any given value. All such controlled phase gates are optimal in the sense that they operate at the maximum possible success probabilities that are achievable within the framework of postselected linear-optical implementations with vacuum ancillas. The quantum gate is implemented by using bulk optical elements and polarization encoding of qubit states. We have experimentally explored the remarkable observation that the optimum success probability is not monotone in the phase.
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