Generation of heralded optical `Schroedinger cat' states by photon-addition

TL;DR

This paper reports the first experimental creation of optical Schr"odinger cat states by photon-addition, achieving high generation rates and fidelity, and demonstrating the technique's robustness even with low-purity squeezed states.

Contribution

It introduces a photon-addition protocol for generating optical Schr"odinger cat states, surpassing previous photon-subtraction methods in rate and control, with potential for repeated applications.

Findings

Generation rate exceeds 8.5 x 10^4 counts/sec

Wigner negativity observed at -8.89 dB squeezing

Maximum fidelity over 80% with cat amplitude |α| ≈ 1.66

Abstract

Optical "Schr\"odinger cat" states, the non-classical superposition of two quasi-classical coherent states, serve as a basis for gedanken experiments testing quantum physics on mesoscopic scales and are increasingly recognized as a resource for quantum information processing. Here, we report the first experimental realization of optical "Schr\"odinger cats" by adding a photon to a squeezed vacuum state, so far only photon-subtraction protocols have been realized. Photon-addition gives us the advantage of using heralded signal photons as experimental triggers, and we can generate "Schr\"odinger cats" at rates exceeding $8.5 \times 10^4$ counts per second; at least one order of magnitude higher than all previously reported realizations. Wigner distributions with pronounced negative parts are demonstrated at down to -8.89 dB squeezing, even when the initial squeezed vacuum input state has low purity. Benchmarking against such a degraded squeezed input state we report a maximum fidelity of more than 80% with a maximum cat amplitude of $|\alpha| \approx 1.66$. Our experiment uses photon-addition from pairs, one of those photons is used for monitoring, giving us enhanced control; moreover the pair production rates are high and should allow for repeated application of photon-addition via repeat-stages.