Spontaneous parametric down-conversion photon sources are scalable in the asymptotic limit for boson-sampling

TL;DR

This paper demonstrates that scalable boson-sampling using multiplexed SPDC photon sources is feasible in the asymptotic limit, with detector efficiency being the primary limiting factor rather than the photon sources themselves.

Contribution

The authors propose a simple architecture for boson-sampling with multiplexed SPDC sources and analyze the conditions under which it remains scalable, emphasizing the role of detector efficiency.

Findings

Photon-number errors are low enough for correct boson-sampling at sufficient detector efficiency.

Detector efficiency must increase exponentially with the number of photons for scalability.

SPDC sources do not limit scalability if detector efficiency is achieved.

Abstract

Boson-sampling has emerged as a promising avenue towards post-classical optical quantum computation, and numerous elementary demonstrations have recently been performed. Spontaneous parametric down-conversion (SPDC) is the mainstay for single-photon state preparation, the technique employed in most optical quantum information processing implementations to-date. Here we present a simple architecture for boson-sampling based on multiplexed SPDC sources and demonstrate that the architecture is limited only by the post-selection detection efficiency assuming that other errors, such as spectral impurity, dark counts, and interferometric instability are negligible. For any given number of input photons, there exists a minimum detector efficiency that allows post selection. If this efficiency is achieved, photon-number errors in the SPDC sources are sufficiently low as to guarantee correct boson-sampling most of the time. In this scheme the required detector efficiency must increase exponentially in the photon number. Thus, we show that idealised SPDC sources will not present a bottleneck for future boson-sampling implementations. Rather, photodetection efficiency is the limiting factor and thus future implementations may continue to employ SPDC sources.