Photonic Quantum Computers

TL;DR

A pivotal moment of photonic quantum computing in the noisy intermediate-scale quantum (NISQ) era is captured, offering insights into how photonic quantum computers might reshape the future of quantum computing.

Abstract

In the pursuit of scalable and fault-tolerant quantum computing architectures, photonic-based quantum computers have emerged as a leading frontier. This article provides a comprehensive overview of advancements in photonic quantum computing, developed by leading industry players, examining current performance, architectural designs, and strategies for developing large-scale, fault-tolerant photonic quantum computers. It also highlights recent groundbreaking experiments that leverage the unique advantages of photonic technologies, underscoring their transformative potential. This review captures a pivotal moment of photonic quantum computing in the noisy intermediate-scale quantum (NISQ) era, offering insights into how photonic quantum computers might reshape the future of quantum computing.

Figures (16)

• Figure 1: The hexagonal waveguide mesh chip was manufactured with the following key features: (a) Design layers, encompassing optical, electrical, and thermal components, were incorporated for both the 7-cell hexagonal waveguide mesh and an auxiliary test cell. (b) The silicon on insulator (SOI) chip, with dimensions of $15\times 20$ mm, was fabricated. (c) A detailed view of the 7-cell hexagonal waveguide mesh, with a scale bar of 2 mm. (d) An enlarged image of an optical interconnection node featuring three tunable basic units (TBUs), with a scale bar of 100 $\mu$m. (e) A close-up image of a single hexagonal cell exhibiting the Mach-Zehnder Interferometer (MZI), with a scale bar of 500 $\mu$m, and additional elements such as tuning heaters and star-type thermal isolation trenches in the right bottom corner. (f) The printed circuit board, where the waveguide mesh chip is mounted and wire bonded for integration. Reproduce from Ref. Ipronics1 under a Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/).
• Figure 2: Integrated Photonic hardware and control architecture of multiuse programmable photonic circuits. (a) The quantity of integrated phase shifters observed in recent waveguide mesh circuits. (b) The architecture of a labeled field programmable photonic gate array (FPPGA), comprising a waveguide mesh core and high-performance building blocks. (c) The FPPGA core incorporates a longitudinally parallel hexagonal waveguide mesh interconnection topology Ipronics2. (d) The electronic control subsystem, signals, and software procedures are depicted, illustrating the mechanisms for controlling the programmable photonic integrated circuit. (e) The data array presents the complete scattering matrix of the FPPGA core, encompassing input and output spatial ports, along with the optical spectral dimension. Key components include GP (general-purpose), MEMA (multichannel electrical monitoring array), MEDA (multichannel electrical driving array), and LU (logic unit). Reproduced from Ref. Ipronics2 under a Creative Commons License (http://creativecommons.org/licenses/by/4.0/).
• Figure 3: The Jiuzhang light-based quantum computing device's configuration, engineered by USTC. The machine operates by intricately manipulating light through an array of optical components. This visual representation of the Jiuzhang photonic network provides insight into its experimental configuration, which occupies an optical table spanning an area of approximately three square meters. Within this setup, 25 Two-Mode Squeezed States (TMSSs) are introduced into the photonic network, resulting in the acquisition of 25 phase-locked light signals. To provide further elucidation, the output modes of the Jiuzhang photonic network are systematically segregated into 100 distinct spatial modes through the employment of miniature mirrors and Polarizing Beam Splitters (PBSs). This accomplishment signifies the emergence of the second quantum computing system to assert the achievement of quantum computational advantages, following in the footsteps of Google's Sycamore quantum processor. Reproduced under the provisions of the Creative Commons license (https://creativecommons.org/licenses/by/4.0/ from Jiuzhang).
• Figure 4: The Jiuzhang 2.0 experiment's configuration. The experiment employs a configuration comprising five key elements. In the top-left quadrant, a high-intensity pulsed laser emitting light at a wavelength of 775 nm is utilized to excite 25 sources of TMSS (Two-mode Squeezed States), as indicated by the orange label within the left section. Simultaneously, a continuous-wave laser operating at 1450 nm is directed to co-propagate with the aforementioned 25 TMSS sources. The resulting 1550-nm two-mode squeezed light is conveyed into a single-mode fiber that demonstrates resistance to temperature variations. Notably, a 5-meter segment of this fiber is wound around a piezo-electric cylinder to enable control over the source phase, located in the central region. Transitioning to the central-right section, an optical arrangement comprising collimators and mirrors facilitates the injection of the 25 TMSSs into a photonic network. Here, 25 light beams corresponding to these TMSSs (illustrated in yellow) with a wavelength of 1450 nm and an intensity power of approximately 0.5 $\mu$W are harnessed for the purpose of achieving phase coherence. The resulting 144 output modes from this arrangement are divided into four segments using arrays of adjustable periscopes and mirrors. Ultimately, these output modes undergo detection using 144 superconducting nanowire single-photon detectors and are subsequently processed through a 144-channel high-speed electronic coincidence unit. Reproduced under Creative Commons license (https://creativecommons.org/licenses/by/4.0/) from Jiuzhang2.0.
• Figure 5: Jiuzhang 3.0: The experimental arrangement comprises 25 stimulated two-mode squeezed state photon sources, synchronized in phase, and directed into a 144-mode ultralow-loss fully-connected optical interferometer. These photons traverse 72 units of fiber loop setups for temporal-spatial demultiplexing before reaching 144 superconducting nanowire single-photon detectors, constituting a pseudo-photon-number resolving detection scheme. Each fiber loop setup, distinguished by distinct colors, accommodates two input modes. Within these setups, photons undergo temporal demultiplexing via fiber beam splitters and delay lines, resulting in four time bins. Furthermore, each time bin is partitioned into two path bins at the terminal fiber beam splitter. Discrimination between photons from the two input modes within the same fiber loop setup is facilitated by assessing their temporal parity through a coincidence event analyzer (not depicted). Reproduced from Jiuzhang3.0 under a Creative Commons licenses (https://creativecommons.org/licenses/by/4.0).