Quantum transport simulations in a programmable nanophotonic processor

Abstract

Environmental noise and disorder play a critical role in quantum particle and wave transport in complex media, including solid-state and biological systems. Recent work has predicted that coupling between noisy environments and disordered systems, in which coherent transport has been arrested due to localization effects, could actually enhance transport. Photonic integrated circuits are promising platforms for studying such effects, with a central goal being the development of large systems providing low-loss, high-fidelity control over all parameters of the transport problem. Here, we fully map out the role of static and dynamic disorder in quantum transport using a low-loss, phase-stable, nanophotonic processor consisting of a mesh of 56 generalized beamsplitters programmable on microsecond timescales. Over 85,600 transport experiments, we observe several distinct transport regimes, including environment-enhanced transport in strong, statically disordered systems. Low loss and programmability make this nanophotonic processor a promising platform for many-boson quantum simulation experiments.Quantum walks (QWs), the coherent analogy to classical random walks, have emerged as a useful model for experimental simulations of quantum transport (QT) phenomena in physical systems. QWs have been implemented in platforms including trapped ions 1,2 , ultra-cold atoms 3 , bulk optics 4-8 and integrated photonics 4,9-16 . Integrated photonic implementations are particularly attractive for relatively large coherence lengths, high interferometric visibilities, integration with single-photon sources 17,18 and detectors 19 , and the promise of scaling to many active and reconfigurable components. The role of static and dynamic disorder in the transport of quantum walkers has been of particular interest in the field of quantum simulation 20,21 .Control over static (time-invariant) and dynamic (timevarying) disorder enables studies of fundamentally interesting and potentially useful QT phenomena in discrete-time (DT) QWs. In systems with strong dynamic disorder, illustrated in Fig. 1(a), a quantum walker evolving over T time steps travels a distance proportional to √ T ; the coherent nature of the quantum walker is effectively erased, resulting in classical, diffusive transport characteristics 22,23 . In contrast, a quantum walker (or coherent wave) traversing an ordered system travels a distance proportional to T as a result of coherent interference between superposition amplitudes -a regime known as ballistic transport (see Fig. 1(b)). Perhaps most notably, a quantum walker propagating through a system with strong, static disorder becomes exponentially localized in space and time, inhibiting transport, as illustrated in Fig. 1(c). This QT phenomena is known as Anderson localization 24 and it has been observed in several systems, including optical media [9][10][11]25,26 . For systems in which transport has been arrested due to Anderson localization, it has recently been predicted that adding environmental noise (dynamic disord...

Classical boson sampling algorithms with superior performance to near-term experiments

“…The advent of integrated quantum photonics 10 has enabled large, complex, stable and programmable optical circuitry 11,12 , while recent advances in photon generation [13][14][15] and detection 16,17 have also been impressive. The possibility to generate many photons, evolve them under a large linear optical unitary transformation, then detect them, seems feasible, so the role of a boson sampling machine as a rudimentary but legitimate computing device is particularly appealing.…”

On-chip continuous-variable quantum entanglement

“…Coupling in and out of the chip is the major contributor to loss and then limits the total amount of entanglement. This can be dramatically reduced by concatenating circuits in a monolithic chip [34,35].…”

“…However, in a recent work, a reprogrammable optical circuit in a single photonic chip where many waveguide interferometers and phase shifters are integrated is applied to the realization of universal linear optics [34,35]. The universal linear optical component is a required element for constructing a fully scalable quantum computer based on KLM scheme together with single photon detectors and single photon sources [33].…”

Generation and manipulation of entangled photons on silicon chips

“…Hence, the stage of integrated quantum photonics research is now moving to hybrid integration on a chip. Among the building blocks, quantum circuits can be realized by using integrated waveguides with cores made of silicon [18,108,110], GaAs [111], or silica-based materials [1,10,13,112]. Of these approaches, silica-based waveguide technology has realized planar lightwave circuits with a significantly large scale for classical optical communication [113,114]; this capability will facilitate the construction of large-scale quantum circuits.…”

“…With the use of waveguides, several quantum tasks have been implemented, from basic quantum optic experiments [1,4,5] to sophisticated quantum information processing such as Shor's algorithm [6], quantum walks [7,8], and boson sampling [9][10][11][12][13][14]. In the future, it is expected that such quantum functional circuits will be integrated on chip with other devices such as photon sources [15,16], functional circuits [17,18], buffers [19], and detectors [20][21][22][23], so that we can realize all optical quantum processors, as shown in Figure 1 [19].…”