Interleaving: Modular architectures for fault-tolerant photonic quantum computing

Abstract

Useful fault-tolerant quantum computers require very large numbers of physical qubits. Quantum computers are often designed as arrays of static qubits executing gates and measurements. Photonic qubits require a different approach. In photonic fusion-based quantum computing (FBQC), the main hardware components are resource-state generators (RSGs) and fusion devices connected via waveguides and switches. RSGs produce small entangled states of a few photonic qubits, whereas fusion devices perform entangling measurements between different resource states, thereby executing computations. In addition to these components, low-loss photonic delays such as optical fiber can be used as fixed-time quantum memories simultaneously storing thousands of photonic qubits. Here, we present a modular architecture for FBQC in which these components are combined to form interleaving modules consisting of one RSG with its associated fusion devices and a few fiber delays. Exploiting the multiplicative power of delay components, each interleaving module can add thousands of physical qubits to the computational Hilbert space. Networks of interleaving modules are universal fault-tolerant quantum computers, which we demonstrate using surface codes and lattice surgery as a guiding example. Our numerical analysis shows that in a network of modules containing 1-km-long fiber delays, a single RSG can generate four logical surface-code qubits with a code distance of 35 while tolerating photon loss rates above 2% in addition to the fiber-delay loss. We illustrate how the combination of interleaving with further uses of non-local fiber connections can reduce the cost of various logical operations and facilitate the implementation of unconventional geometries such as periodic boundaries or stellated surface codes. Interleaving applies beyond purely optical architectures, and can also turn many small disconnected matter-qubit devices with transduction to photons into a large-scale quantum computer.

Switch networks for photonic fusion-based quantum computing

“…Furthermore, it is easily seen that this example is not related to the constructions from Sec. IIIB since the only possibility would be the GMZI implementing G( [6]) ∼ = G( [3,2]), for which individual phase settings range on six values (compared to three in Table II).…”

“…An entire quantum computer can be constructed using networked modules, each comprised of an RSG and associated fusion devices. The approach of interleaving, introduced recently in [2], provides a technique for implementing fault-tolerant quantum computation using these modules in the context of photonic FBQC (meeting some common objectives as Ref. [3] for example for other quantumcomputing paradigms).…”

Fault-tolerant resource estimate for quantum chemical simulations: Case study on Li-ion battery electrolyte molecules

“…[13,14]. On the other hand, the fully-compiled resource estimate is markedly different to prior studies, in that it makes use of the fusion-based quantum computation (FBQC) scheme [16,17].…”

“…A salient feature of the photon-based FBQC scheme is the possibility of interleaving [17]. Photons can be stored in an optical delay line of large length without significantly degrading the quality of the photonic qubits.…”

Low-overhead fault-tolerant quantum computing using long-range connectivity

“…Recently, however, there has been significant progress in developing long-ranged entangling gate operations in a variety of quantum processing systems, including those based on superconductors [25], semiconductors [26][27][28], and trapped ions [29,30]. Optical photons provide an approach that is not naturally constrained to a local two-dimensional layout [31,32], and can also allow for other qubit systems to be connected into complex quantum networks [33][34][35][36][37][38]. The possibility of long-range connectivity opens the door to a new class of quantum codes and fault-tolerant architectures that can harness this connectivity to our advantage.…”