Real-Time Shaping of Entangled Photons by Classical Control and Feedback

Abstract

We present a novel method for compensating scattering of entangled photons in real-time, by using feedback from the classical pump beam that stimulates their creation, paving the way for implementing wavefront shaping in quantum technologies.

Pump-shaping of non-collinear and non-degenerate entangled photons

“…We generalize the derivation in Ref. [14] for the cases of non-collinear and non-degenerate entangled photons. Generally, the quantum state of the entangled photons is given by |ψ = dq s dq i dω s dω i ψ(q s , q i , ω s , ω i )a † (q s , ω s )a † (q i , ω i )|0 where a † (q, ω) is the creation operator of a photon with a transverse wavevector q and frequency ω, |0 is the vacuum state, and we assume the signal and idler photons have the same polarization [19].…”

“…We experimentally demonstrate this result by optimizing the correlations between entangled photons generated via non-collinear SPDC and scattered by a thin diffuser. For non-degenerate SPDC, we show that even though the wavelengths of the two entangled photons are different, energy conservation ensures the surprising correspondence between the intensity of the pump beam and the quantum correlations between the entangled photons, allowing the use of the pump-shaping method [14]. We experimentally demonstrate optimization of entangled photons separated by nearly 100nm.…”

“…A promising approach to compensate the scattering of single and entangled photons is to borrow concepts from the well-established fields of adaptive optics [6] and wavefront shaping [7,8], and apply them to quantum links. To this end, methods for shaping the wavefront of single and entangled photons using spatial light modulators (SLMs) have been demonstrated, either by controlling the photons directly [9][10][11], or tailoring the classical pump beam that stimulates their creation via spontaneous parametric down conversion (SPDC) [12][13][14]. Recently, a pumpshaping method in which the intensity of the classical pump beam is used as feedback for compensating the scattering of entangled photons has been demonstrated, allowing for realtime optimization of entangled photons [14].…”

“…To this end, methods for shaping the wavefront of single and entangled photons using spatial light modulators (SLMs) have been demonstrated, either by controlling the photons directly [9][10][11], or tailoring the classical pump beam that stimulates their creation via spontaneous parametric down conversion (SPDC) [12][13][14]. Recently, a pumpshaping method in which the intensity of the classical pump beam is used as feedback for compensating the scattering of entangled photons has been demonstrated, allowing for realtime optimization of entangled photons [14]. However, this demonstration was realized only in a collinear and frequency-degenerate configuration of SPDC, which limits the range of possible applications.…”

Quantum key distribution over scattering channel

“…Hao et al proposed a DOPC scheme to increase the channel efficiency of a classical optical communication system in 2014 [33]. And the task of shaping or monitoring quantum states after scattering media has attracted much attention recently [34,35]. However, applying the wavefront shaping methods in QKD through scattering channels has rarely been studied.…”