Quantum mechanics promises computational powers beyond the reach of classical computers. Current technology is on the brink of an experimental demonstration of the superior power of quantum computation compared to classical devices. For such a demonstration to be meaningful, experimental noise must not affect the computational power of the device; this occurs when a classical algorithm can use the noise to simulate the quantum system. In this work, we demonstrate an algorithm which simulates boson sampling, a quantum advantage demonstration based on many-body quantum interference of indistinguishable bosons, in the presence of optical loss. Finding the level of noise where this approximation becomes efficient lets us map out the maximum level of imperfections at which it is still possible to demonstrate a quantum advantage. We show that current photonic technology falls short of this benchmark. These results call into question the suitability of boson sampling as a quantum advantage demonstration.
We study the quantum to classical transition in boson sampling by analyzing how
N-boson interference is affected by inevitable noise in an experimental setup. We adopt the Gaussian noise model of Kalai and Kindler for boson sampling and show that it appears from some realistic experimental imperfections. We reveal a connection between noise in boson sampling and partial distinguishability of bosons, which allows us to prove efficient classical simulatability of noisy no-collision boson sampling with finite noise amplitude $\ensuremath{\epsilon}$, i.e., $\ensuremath{\epsilon}=\mathrm{\ensuremath{\Omega}}(1)$ as $N\ensuremath{\rightarrow}\ensuremath{\infty}$. On the other hand, using an equivalent representation of network noise as losses of bosons compensated by random (dark) counts of detectors, it is proven that for noise amplitude inversely proportional to total number of bosons, i.e., $\ensuremath{\epsilon}=O(1/N)$, noisy no-collision boson sampling is as hard to simulate classically as in the noiseless case. Moreover, the ratio of ``noise clicks'' (lost bosons compensated by dark counts) to the total number of bosons
N vanishes as $N\ensuremath{\rightarrow}\ensuremath{\infty}$ for arbitrarily small noise amplitude, i.e., $\ensuremath{\epsilon}=o(1)$ as $N\ensuremath{\rightarrow}\ensuremath{\infty}$; hence, we conjecture that such a noisy boson sampling is also hard to simulate classically. The results significantly relax the sufficient condition on noise in network components, such as two-mode beam splitters, for classical hardness of experimental boson sampling