Boosted linear-optical measurements on single-rail qubits with unentangled ancillas
This work addresses a bottleneck in quantum information processing with optical qubits, offering a practical improvement for quantum measurements.
The paper tackled the challenge of performing quantum logic on single-rail qubits in optical systems, which is difficult due to weak nonlinearities, and achieved a success probability of 147/256 for measurements in the XY Bloch plane, surpassing the previous limit of 1/2.
Any quantum state of the radiation field, sliced in small non-overlapping space-time bins is a collection of single-rail qubits, each spanning the vacuum and single-photon Fock state of a mode. Quantum logic on these qubits would enable arbitrary measurements on information-bearing light, but is hard due to the lack of strong nonlinearities. With unentangled ancilla single-rail qubits, an $8$-port interferometer and photon detection, we show any single-rail qubit measurement in the $XY$ Bloch plane is realizable with success probability $147/256$, which beats the prior-known $1/2$ limit.