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Scalable boson-sampling with time-bin encoding using a loop-based architecture
Keith R. Motes, Alexei Gilchrist, Jonathan P. Dowling, Peter P. Rohde
TL;DR
Large-scale optical quantum computing faces daunting physical resource requirements. This paper presents boson-sampling with time-bin photons in two nested fiber loops, using dynamically controlled coupling ratios to construct linear-optics interferometers. The architecture has fixed experimental complexity as interferometer size grows, with scalability limited by fiber and switch transmission efficiencies.
Problem
Full-fledged linear optics quantum computing may require millions of optical elements, motivating approaches that use fewer physical resources.
Source: p. 1Method
The architecture sends a pulse train of single photons through nested fiber loops whose dynamically controlled coupling ratios implement the required linear-optics operations.
Source: pp. 2–3Results
The presented architecture is arbitrarily scalable with constant experimental complexity independent of interferometer size, while scalability is limited by fiber and switch transmission efficiencies.
Source: pp. 4–5Takeaways & Limitations
A single point of interference suggests the architecture may be easier to stabilize than approaches based on waveguides or discrete elements.
Source: p. 5Constructing large interferometers requires exponentially small fiber-loop loss rates, although the cited discussion notes conventional spatial implementations face the same issue.
Source: p. 4
Abstract
from arXiv · showhide
We present an architecture for arbitrarily scalable boson-sampling using two nested fiber loops. The architecture has fixed experimental complexity, irrespective of the size of the desired interferometer, whose scale is limited only by fiber and switch loss rates. The architecture employs time-bin encoding, whereby the incident photons form a pulse train, which enters the loops. Dynamically controlled loop coupling ratios allow the construction of the arbitrary linear optics interferometers required for boson-sampling. The architecture employs only a single point of interference and may thus be easier to stabilize than other approaches. The scheme has polynomial complexity and could be realized using demonstrated present-day technologies.
Appendix A: Alternate proof for universality
The appendix establishes universality by showing that two consecutive loops can implement any pairwise beamsplitter interaction for three modes, then extending the argument inductively to arbitrary n.
Appendix A: Alternate proof for universality
- For n = 3, two consecutive loops implement arbitrary beamsplitter interactions between modes 1–2, 1–3, or 2–3.Dynamically controlled switching lets some beamsplitters perform permutations while one performs the desired interaction.Source: Appendix A · p. 5, Figure 6 · p. 6
- The n = 3 construction is the base case for the generalization from n modes to n + 1 modes.The induction uses an n-mode unitary, routes one selected mode to interact with the additional mode, and reverses the permutation.Source: Appendix A · p. 5, Figure 7 · p. 7
- For arbitrary n, universality follows inductively: an n-mode unitary and permutations allow an arbitrary beamsplitter operation between any pair of modes.The induction step routes a chosen one of the first n modes to interact with mode n + 1, then applies the inverse permutation.Source: Appendix A · p. 5, Figure 7 · p. 7