A perspective on silicon photonic quantum computing with spin qubits
Andreas Theo Pfenning, Xiruo Yan, Sebastian Gitt, Joshua Fabian, Becky Lin, Donald M. Witt, Abdelrahman E. Afifi, Adan Azem, Adam Darcie, Jingda Wu, Matthew Mitchell, Kashif M. Awan, Lukas Chrostowski, Jeff F. Young
We recently proposed a quantum computing platform that exploits circuit-bound photons to create cluster states and achieve one-way measurement-based quantum computations on arrays of photonically interfaced solid-state spin qubits with long coherence-times. Single photons are used for spin initialization, readout and for photon-mediated long-range entanglement creation. In this conference talk, we elaborate on the challenges that are faced during any practical implementation of this architecture by breaking it down into the key physical building blocks. We further discuss the constraints imposed on the spin qubits and the photonic circuit components that are set by the requirements of achieving fault-tolerant performance.
We recently proposed a quantum computing platform that exploits circuit-bound photons to create cluster states and achieve one-way measurement-based quantum computations on arrays of photonically interfaced solid-state spin qubits with long coherence-times. Single photons are used for spin initialization, readout and for photon-mediated long-range entanglement creation. In this conference talk, we elaborate on the challenges that are faced during any practical implementation of this architecture by breaking it down into the key physical building blocks. We further discuss the constraints imposed on the spin qubits and the photonic circuit components that are set by the requirements of achieving fault-tolerant performance.
Universal quantum computing holds the promise to fundamentally change today’s information-based society, yet a hardware platform that will provide a clear path to fault-tolerant quantum computing remains elusive. One recently proposed platform involves the use of circuit-bound photons to build cluster states and perform one-way measurement-based quantum computations on arrays of long-coherence-time solid-state spin qubits. Herein, we discuss the challenges that are faced during any practical implementation of this architecture by itemizing the key physical building blocks and the constraints imposed on the spin qubits and the photonic circuit components by the requirements of fault-tolerant performance. These considerations point to silicon as a leading candidate to host such a platform, and a roadmap for developing a silicon photonic circuit-based platform for measurement-based, fault-tolerant universal quantum computing is offered.
Photons are excellent carriers of quantum information; their polarization remains coherent for long times and it is easy to measure and precisely rotate. The fundamental hurdle with photon-based quantum information processing is the lack of direct photon-photon interactions to provide entanglement between pairs of photons. Recent proposals show the ability to build large cluster states from small entangled states using non-deterministic operations, but the generation of deterministic high-fidelity small entangled states remains a challenge. In this talk, we will show how the necessary cluster-state building blocks for large-scale quantum computation can be created from coupled solid-state quantum emitters without the need for any two-qubit gates and regardless of whether the emitters are identical. We provide a recipe for the generation of two-dimensional, ‘cluster-state’ entangled photons that can be carried out with existing experimental capabilities.
This is a short overview explaining how building a large-scale, silicon-photonic quantum computer has been reduced to the creation of good sources of 3-photon entangled states (and may simplify further). Given such sources, each photon needs to pass through a small, constant, number of components, interfering with at most 2 other spatially nearby photons, and current photonics engineering has already demonstrated the manufacture of thousands of components on two-dimensional semiconductor chips with performance that, once scaled up, allows the creation of tens of thousands of photons entangled in a state universal for quantum computation. At present the fully integrated, silicon-photonic architecture we envisage involves creating the required entangled states by starting with single-photons produced non-deterministically by pumping silicon waveguides (or cavities) combined with on-chip filters and nanowire superconducting detectors to herald that a photon has been produced. These sources are multiplexed into being near-deterministic, and the single photons then passed through an interferometer to non-deterministically produce small entangled states—necessarily multiplexed to near-determinism again. This is followed by a “ballistic” scattering of the small-scale entangled photons through an interferometer such that some photons are detected, leaving the remainder in a large-scale entangled state which is provably universal for quantum computing implemented by single-photon measurements. There are a large number of questions regarding the optimum ways to make and use the final cluster state, dealing with static imperfections, constructing the initial entangled photon sources and so on, that need to be investigated before we can aim for millions of qubits capable of billions of computational time steps. The focus in this article is on the theoretical side of such questions.
General purpose quantum computers will utilize millions of physical qubits, thus requiring an underlying qubit technology that can be manufactured at scale. Integrated silicon photonics is an intrinsically scalable and manufacturable platform where all necessary gates are available to manipulate qubits, encoded in photons, with very high fidelity and low noise. In this talk, we will discuss architectures for fault-tolerant quantum computing with photonics in the newly-introduced fusion-based quantum computing paradigm. Fusion-based quantum computing presents a new framework for fault-tolerant quantum computation, focused on the efficient integration of quantum error correction and physical-level hardware operations. Its primitives, small entangled resource states and projective entangling gates, make it particularly useful in an integrated photonics platform, offering significant architectural simplifications and reducing requirements on physical level operations.
Spin qubits in silicon quantum dot arrays are a promising quantum computation platform for long-term scalability due to their small qubit footprint and compatibility with advanced semiconductor manufacturing. However, spin qubit devices face a key architectural bottleneck: the large physical footprint of readout components relative to qubits prevents a dense layout where all qubits can be measured simultaneously, complicating the implementation of quantum error correction. This challenge is offset by the platform's unique rapid shuttling capability, which can be used to transport qubits to distant readout ports. In this work, we explore the design constraints and capabilities of spin qubits in silicon and propose the SNAQ (Shuttling-capable Narrow Array of spin Qubits) surface code architecture, which relaxes the 1:1 readout-to-qubit assumption by leveraging spin shuttling to time-multiplex ancilla qubit initialization and readout. Our analysis shows that, given sufficiently high (experimentally demonstrated) qubit coherence times, SNAQ delivers an orders-of-magnitude reduction in chip area per logical qubit. Additionally, by using a denser grid of physical qubits, SNAQ enables fast transversal logic for short-distance logical operations, achieving over 10x improvement in local logical clock speed while still supporting global operations via lattice surgery. This translates to a 3.2-5.7x improvement in key Adder and Lookup fault-tolerant subroutines. Our work pinpoints critical hardware metrics and provides a compelling path toward high-performance fault-tolerant computation on near-term-manufacturable spin qubit arrays.
The scaling barriers currently faced by both quantum networking and quantum computing technologies ultimately amount to the same core challenge of distributing high-quality entanglement at scale. In this Perspective, a novel quantum information-processing architecture based on optically active spins in silicon is proposed that offers a combined single technological platform for scalable fault-tolerant quantum computing and networking. The architecture is optimized for overall entanglement distribution and leverages color-center spins in silicon (T centers) for their manufacturability, photonic interface, and high-fidelity information-processing properties. Silicon nanophotonic optical circuits allow for photonic links between T centers, which are networked via telecom-band optical photons in a highly connected graph. This high connectivity unlocks the use of low-overhead quantum error-correcting codes, significantly accelerating the time line for modular scalable fault-tolerant quantum repeaters and quantum processors. Published by the American Physical Society 2024