Two-photon phase-sensing with single-photon detection

Abstract

Path-entangled multi-photon states allow optical phase-sensing beyond the shot-noise limit, provided that an efficient parity measurement can be implemented. Realising this experimentally is technologically demanding, as it requires coincident single-photon detection proportional to the number of photons involved, which represents a severe challenge for achieving a practical quantum advantage over classical methods. Here, we exploit advanced quantum state engineering based on superposing two photon-pair creation events to realise a new approach that bypasses this issue. In particular, optical phase shifts are probed with a two-photon quantum state whose information is subsequently effectively transferred to a single-photon state. Notably, without any multiphoton detection, we infer phase shifts by measuring the average intensity of the single-photon beam on a photodiode, in analogy to standard classical measurements. Importantly, our approach maintains the quantum advantage: twice as many interference fringes are observed for the same phase shift, corresponding to N = 2 path-entangled photons. Our results demonstrate that the advantages of quantum-enhanced phase-sensing can be fully exploited in standard intensity measurements, paving the way towards resource-efficient and practical quantum optical metrology.

A silicon source of heralded single photons at 2 μm

“…12,13 Entangled photons have been used to demonstrate new imaging and spectroscopy techniques that are able to get rid of detection technology limitations, namely, ghost imaging 14,15 or an undetected photon measurement. [16][17][18] To enable quantumenhanced MIR metrology leveraging these quantum-based measurement strategies, a source of single or entangled photons beyond 2 μm is required. Up until now, these techniques have been investigated only with bulky, alignment tolerant, and expensive instrumentation based on free space nonlinear crystals.…”

Phase Sensitivity Improvement in Correlation-Enhanced Nonlinear Interferometers

“…Due to its special quantum characteristic, the SUI has attracted the attention of researchers successfully. In addition, it can apply in quantum metrology, quantum information, quantum state engineering, and quantum imaging [63][64][65][66][67], especially the ones with the spontaneous parametric down-conversion regime [68][69][70][71]. (See [39,72,73] for latest reviews on SU(1,1) interferometers.…”

Loss compensated and enhanced mid-infrared interaction-free sensing with undetected photons

“…* n.gemmell20@imperial.ac.uk Much effort in recent years in the field of induced coherence has involved simplifying the methodology and apparatus to make the technique more accessible. This has resulted in the implementation of 'folded' systems which use a double pass of a single nonlinear crystal [8][9][10][11], a seeded version of the experiment [12], an interferometer that uses two different nonlinear processes [13], and spectroscopy based on all fields passing stacked crystals [14]. This work continues to push the technology closer to real-world applications [15].…”