I introduce time-reflection photonic quantum computing, an architecture in which qubits are encoded in pairs of counter-propagating photonic modes that evolve along dual temporal channels. By engineering gates that implement time reflections between these channels, the dynamics become intrinsically reversible, causing dominant error processes—dephasing, photon loss, and phase noise—to be continuously unwound and rephased without external feedback or active error-correction cycles. This built-in self-correction enables ultra-low-energy quantum information processing at room temperature and substantially reduces hardware complexity compared with superconducting or trapped-ion platforms. My analytical modeling and numerical simulations show that time-reflection circuits preserve coherence over large depths, maintain high fidelities in the presence of realistic noise, and support the implementation of a universal gate set using photonic resources. These results establish time-reflection photonic architectures as a promising, energy-efficient route toward scalable quantum information processing.
I introduce time-reflection photonic quantum computing, an architecture in which qubits are encoded in pairs of counter-propagating photonic modes that evolve along dual temporal channels. By engineering gates that implement time reflections between these channels, the dynamics become intrinsically reversible, causing dominant error processes—dephasing, photon loss, and phase noise—to be continuously unwound and rephased without external feedback or active error-correction cycles. This built-in self-correction enables ultra-low-energy quantum information processing at room temperature and substantially reduces hardware complexity compared with superconducting or trapped-ion platforms. My analytical modeling and numerical simulations show that time-reflection circuits preserve coherence over large depths, maintain high fidelities in the presence of realistic noise, and support the implementation of a universal gate set using photonic resources. These results establish time-reflection photonic architectures as a promising, energy-efficient route toward scalable quantum information processing.
Abstract I introduce time-reflection photonic quantum computing, an architecture in which qubits are encoded in pairs of counterpropagating photonic modes that evolve along dual temporal channels. By engineering gates that implement time reflections between these channels, the dynamics become intrinsically reversible, causing dominant error processes—dephasing, photon loss, and phase noise—to be continuously unwound and rephased without external feedback or active errorcorrection cycles. This builtin selfcorrection enables ultralowenergy quantum information processing at room temperature and substantially reduces hardware complexity compared with superconducting or trappedion platforms. My analytical modeling and numerical simulations show that timereflection circuits preserve coherence over large depths, maintain high fidelities in the presence of realistic noise, and support the implementation of a universal gate set using photonic resources. These results establish timereflection photonic architectures as a promising, energyefficient route toward scalable quantum information processing.
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.
Fault-tolerant quantum computing requires architectures that simultaneously address scalability, connectivity, and error correction under realistic noise constraints. We present a compound photonic-atomic quantum computing platform that uses cavity QED to realize near-deterministic entangling operations between flying photonic qubits and stationary atomic qubits. Photons provide long-range connectivity and scalability via measurement-based quantum computing (MBQC), while atoms supply reusable, near-deterministic resources for photon generation and entanglement, overcoming the inefficiency of purely photonic platforms. The core primitive is a symmetrized Duan-Kimble photon-atom controlled-phase (CZ) gate, robust to experimental imperfections and high-fidelity. Using single 87Rb atoms coupled to optical cavities, we give protocols for state preparation, measurement, photon generation, and entangling gates on tens-of-nanosecond timescales, and show how large-scale cluster states with effectively unrestricted connectivity and reduced overhead can be generated through atomic reuse. We analyze fault tolerance on the Raussendorf-Harrington-Goyal (RHG) lattice with a hardware-aware noise model capturing asymmetric loss and correlated photonic-atomic errors. Logical memory simulations yield a photon-loss threshold near 2.6% per physical gate ($\sim$15\% total per trajectory). The full Clifford set -- Hadamard, phase, CNOT -- is implementable transversally or fold-transversally at thresholds matching the identity channel, and we propose two non-Clifford resource-state routes (code teleportation and magic state cultivation) within the foliated cluster-state architecture.
Hybridizing different degrees of freedom or physical platforms potentially offers various advantages in building scalable quantum architectures. Here, we introduce a fault-tolerant hybrid quantum computation by building on the advantages of both discrete-variable (DV) and continuous-variable (CV) systems. In particular, we define a CV-DV hybrid qubit with a bosonic cat code and a single photon, which is implementable in current photonic platforms. Due to the cat code encoded in the CV part, the predominant loss errors are readily correctable without multiqubit encoding, while the logical basis is inherently orthogonal due to the DV part. We design fault-tolerant architectures by concatenating hybrid qubits and an outer DV quantum error-correction code such as a topological code, exploring their potential merit in developing scalable quantum computation. We demonstrate by numerical simulations that our scheme is at least an order of magnitude more resource efficient compared to all previous proposals in photonic platforms, allowing us to achieve a record-high loss threshold among existing CV and hybrid approaches. We discuss the realization of our approach not only in all-photonic platforms but also in other hybrid platforms including superconducting and trapped-ion systems, which allows us to find various efficient routes toward fault-tolerant quantum computing. Published by the American Physical Society 2024
Quantum error correction (QEC) is indispensable for scalable quantum computing, but implementing it with minimal hardware overhead remains a central challenge. Large spin systems with collective degrees of freedom offer a promising route to reducing the control complexity of qubit architectures while retaining a large Hilbert space for fault-tolerant encoding. However, existing proposals for logical gates and QEC in spin ensembles generally rely on inefficient higher-order interactions. Here we introduce spin-N-Cat codes, which encode logical qubits in superpositions of spin-coherent states and generalize bosonic Cat codes to the modular subspaces of permutationally symmetric spin ensembles. The code corrects collective and individual dephasing, excitation, and decay errors. We also present an efficient physical realization in central-spin systems, such as a quantum dot, where encoding, decoding, and a universal, fault-tolerant, and bias-preserving gate set are implemented using only first-order interactions. Numerical simulations demonstrate high logical fidelity under dephasing and excitation-decay noise, independent of noise bias, and that full QEC cycles are feasible with realistic microscopic parameters. For the large collective spins available in quantum dots, this translates into a substantial extension of coherence time. Our results establish spin-N-Cat codes as a scalable, hardware-efficient approach to QEC in spin-based quantum architectures.
Photonic quantum computing is one of the leading approaches to universal quantum computation. However, large-scale implementation of photonic quantum computing has been hindered by its intrinsic difficulties, such as probabilistic entangling gates for photonic qubits and lack of scalable ways to build photonic circuits. Here, we discuss how to overcome these limitations by taking advantage of two key ideas which have recently emerged. One is a hybrid qubit-continuous variable approach for realizing a deterministic universal gate set for photonic qubits. The other is the time-domain multiplexing technique to perform arbitrarily large-scale quantum computing without changing the configuration of photonic circuits. These ideas together will enable scalable implementation of universal photonic quantum computers in which hardware-efficient error correcting codes can be incorporated. Furthermore, all-optical implementation of such systems can increase the operational bandwidth beyond terahertz in principle, ultimately enabling large-scale fault-tolerant universal quantum computers with ultrahigh operation frequency.