2018/09/30 by Thomas Kilmer, Saikat Guha
Physics and Astronomy · #quant-ph
paper · pdf · doi:10.1103/physreva.99.032302
published as Phys. Rev. A 99, 032302 (2019) · 13 pages, 10 figures
arxiv created 2018/11/28 · arxiv updated 2019/03/06
Linear optical realizations of Bell state measurement (BSM) on two single-photon qubits succeed with probability ps no higher than 0.5. However pre-detection quadrature squeezing, i.e., quantum noise limited phase sensitive amplification, in the usual linear-optical BSM circuit, can yield ps ≈ 0.643. The ability to achieve ps > 0.5 has been found to be critical in resource-efficient realizations of linear optical quantum computing and all-photonic quantum repeaters. Yet, the aforesaid value of ps > 0.5 is not known to be the maximum achievable using squeezing, thereby leaving it open whether close-to-100% efficient BSM might be achievable using squeezing as a resource. In this paper, we report new insights on why squeezing-enhanced BSM achieves ps > 0.5. Using this, we show that the previously-reported ps ≈ 0.643 at single-mode squeezing strength r=0.6585---for unambiguous state discrimination (USD) of all four Bell states---is an experimentally unachievable point result, which drops to ps ≈ 0.59 with the slightest change in r. We however show that squeezing-induced boosting of ps with USD operation is still possible over a continuous range of r, with an experimentally achievable maximum occurring at r=0.5774, achieving ps ≈ 0.596. Finally, deviating from USD operation, we explore a trade-space between ps, the probability with which the BSM circuit declares a "success", versus the probability of error pe, the probability of an input Bell state being erroneously identified given the circuit declares a success. Since quantum error correction could correct for some pe > 0, this tradeoff may enable better quantum repeater designs by potentially increasing the entanglement generation rates with ps exceeding what is possible with traditionally-studied USD operation of BSMs.