High-fidelity linear optical quantum computing with polarization encoding (11 pages)

AG White, TB Bell, NK Langford +4 more

Federico M. Spedalieri, Hwang Lee, Jonathan P. Dowling

We demonstrate how to implement the KLM scheme for linear optical quantum computing using polarization encoding. The resulting gates have very high fidelity and allow construction of optical cluster states with currently available detectors.

Sam Morley-Short

Federico M. Spedalieri, Hwang Lee, Jonathan P. Dowling

We show that the KLM scheme [Knill, Laflamme, and Milburn, Nature 409, 46 (2001)] can be implemented using polarization encoding, thus reducing the number of path modes required by half. One of the main advantages of this new implementation is that it naturally incorporates a loss detection mechanism that makes the probability of a gate introducing a non-detected error, when non-ideal detectors are considered, dependent only on the detector dark-count rate and independent of its efficiency. Since very low dark-count rate detectors are currently available, a high-fidelity gate (probability of error of order ${10}^{\ensuremath{-}6}$ conditional on the gate being successful) can be implemented using polarization encoding. The detector efficiency determines the overall success probability of the gate but does not affect its fidelity. This can be applied to the efficient construction of optical cluster states with very high fidelity for quantum computing.

John Calsamiglia

Federico M. Spedalieri, Jonathan P. Dowling, Hwang Lee

Federico M. Spedalieri, Jonathan P. Dowling, and Hwang Lee Abstract We present a detailed description of nondeterministic quantum logic gates: the crucial component of linear optical quantum computing. We use the qubits that are encoded in the polarization degrees of freedom, as opposed to the original dual-rail encoding. Employing the polarization-encoding scheme, we can avoid the undetected errors due to the inefficiency of the photodetectors and, therefore, achieve high gate fidelity, independent of the quantum efficiency of the detectors. Furthermore, we show that such a high-fidelity gate operation can be performed with no need of number-resolving detectors.