Sub-Shot-Noise Transmission Measurement Enabled by Active Feed-Forward of Heralded Single Photons

Abstract

Harnessing the unique properties of quantum mechanics offers the possibility to deliver new technologies that can fundamentally outperform their classical counterparts. These technologies only deliver advantages when components operate with performance beyond specific thresholds. For optical quantum metrology, the biggest challenge that impacts on performance thresholds is optical loss. Here we demonstrate how including an optical delay and an optical switch in a feed-forward configuration with a stable and efficient correlated photon pair source reduces the detector efficiency required to enable quantum enhanced sensing down to the detection level of single photons. When the switch is active, we observe a factor of improvement in precision of 1.27 for transmission measurement on a per input photon basis, compared to the performance of a laser emitting an ideal coherent state and measured with the same detection efficiency as our setup. When the switch is inoperative, we observe no quantum advantage.Quantum mechanics quantifies the highest precision that is achievable in each type of optical measurement [1][2][3]. Single photon probes measured with single photon detectors are in principle optimal for gaining the most precision per-unit intensity when measuring optical transmission [4]. However, in practice, optical loss and low component efficiencies prevent an advantage from being achieved using single photon detectors [5]. One way to reduce the impact of lower component efficiency is to incorporate fast optical switching and an optical delay with schemes that are based on heralded generation of quantum sates [6]. This then enables use of a quantum state conditioned on the successful detection of a correlated signal -this is referred to as feed-forward.Feed-forward is key for demonstrations of optical quantum computing [7], it has been used in experiments that increase the generation rate [8][9][10][11][12] and signal-to-noise ratio [13] of heralded single photons, it has been used to calibrate single photon detectors [14] and it has also been applied to gather evidence of single photon sensitivity in animal vision [15]. Jakeman and Rarity proposed in Ref.[6] using feed-forward with correlated photon pairs to enable sub shot noise optical transmission measurements when component efficiency is otherwise not sufficient to permit a quantum advantage in passive direct detection [16][17][18]. But despite becoming identified as key to more general multi-photon entangled quantum state engineering for quantum metrology [19,20], feed-forward has not been implemented for quantum enhanced parameter estimation. Here we implement the proposal featured in Ref.[6] (Fig. 1) to realise sub shot noise measurement of transmissitivity, using single photon detectors that are too low in efficiency to enable sub shot noise performance in a passive measurement.The transmissivity η of a sample is in general estimated by measuring the reduction of light intensity from a known mean input valueN in , to a reduced mean valueN out according ...

Efficient excitation of dye molecules for single photon generation

“…When we convolve equation (9) with a Gaussian to represent the jitter, we obtain the red curve which gives S=0.5 and N 1.25 eff = . The corresponding de-convolved g (2) (0) is 0.2. Further, there is a background-about 10% of the peak molecule count rate found from a region of anthracene with no molecule present in a confocal scan-that generates some accidental coincidences.…”

“…Many applications have need of a fast, reliable source of individual photons on demand [1]. These range from quantum sensing [2] through quantum communication [3] to full-scale photonic quantum computing [4]. The standard way to obtain single photons is to make a pair by parametric down conversion or spontaneous fourwave mixing, and use the detection of one photon to herald the presence of the other.…”

Quantum Sensing of Absorbance and the Beer-Lambert Law

“…2(a) for a fixed L = 1 and no experimental loss η l = 1, along with the quantum advantage Q(a) = F Q (a)/F C (a). We see that fixing L provides a scaling for Q(a) that follows the trend of absorption estimation, namely that Q(a) → ∞ for a → 0 (Q(η) → ∞ for η → 1) [11]. We see in For a varying length we see that both F C (a) and F Q (a) have maximal values before tending towards zero for both large and small L. This demonstrates that for a particular a (e.g.…”

“…Optical quantum metrology investigates how quantum strategies, such as probing with quantum states of light, provides increased precision over classical techniques in estimating parameters including optical phase [9,10], transmission [11,12], polarisation [13], and displacements [14]. A variety of practical implementations have demonstrated these schemes and have been shown to outperform classical strategies operating at the same average input intensity [15].…”

Fibre-integrated noise gating of high-purity heralded single photons

“…In addition, correlation between the signal and idler modes can be used to gate desired events, either electronically through post-selecting coincident detection signals [13], or optically by feed-forward from the heralding detection to a fast optical switch [14]. The latter is more desirable as it reduces, rather than masks, the flux of unwanted photons delivered at the output of the source -important for measurements that are limited by total photon budget [15,16].…”