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High-fidelity multi-qubit gates are a critical resource for near-term quantum computing, as they underpin the execution of both quantum algorithms and fault-tolerant protocols. The Toffoli gate (CCNOT), in particular, plays a central role…

Quantum Physics · Physics 2025-09-09 M. AbuGhanem

Quantum error-correcting codes, such as subspace, subsystem, and Floquet codes, are typically constructed within the stabilizer formalism, which does not fully capture the idea of fault-tolerance needed for practical quantum computing…

Quantum Physics · Physics 2025-11-12 Peter-Jan H. S. Derks , Alex Townsend-Teague , Ansgar G. Burchards , Jens Eisert

The initialization of quantum states or Quantum State Preparation (QSP) is a basic subroutine in quantum algorithms. In the worst case, general QSP algorithms are expensive due to the application of multi-controlled gates required to build…

A fault-tolerant way to prepare logical code-states of Q1 codes, i.e., quantum polar codes encoding one qubit, has been recently proposed. The fault tolerance therein is guaranteed by an error detection gadget, where if an error is detected…

Quantum Physics · Physics 2025-03-12 Ashutosh Goswami , Mehdi Mhalla , Valentin Savin

Quantum error-correcting codes are a vital technology for demonstrating reliable quantum computation. They require data qubits for encoding quantum information and ancillary qubits for taking error syndromes necessary for error correction.…

Quantum Physics · Physics 2025-08-12 Shintaro Sato , Yasunari Suzuki

Code switching is an established technique that facilitates a universal set of FT quantum gate operations by combining two QEC codes with complementary sets of gates, which each by themselves are easy to implement fault-tolerantly. In this…

Quantum Physics · Physics 2025-09-10 Sascha Heußen , Janine Hilder

Current proposals for quantum compilers require the synthesis and optimization of linear reversible circuits and among them CNOT circuits. Since these circuits represent a significant part of the cost of running an entire quantum circuit,…

The development of a continuous-variable photonic quantum computer depends on the reliable preparation of high-quality Gottesman-Kitaev-Preskill states. The most promising GKP preparation scheme is the cat breeding protocol, which can…

Quantum Physics · Physics 2025-08-11 Olga Solodovnikova , Ulrik L. Andersen , Jonas S. Neergaard-Nielsen

Fault tolerance is widely regarded as indispensable for achieving scalable and reliable quantum computing. However, the spacetime overhead required for fault-tolerant quantum computating remains prohibitively large. A critical challenge…

Quantum Physics · Physics 2025-11-26 Pei Zeng , Guo Zheng , Qian Xu , Liang Jiang

We present improved quantum circuit for modular exponentiation of a constant, which is the most expensive operation in Shor's algorithm for integer factorization. While previous work mostly focuses on minimizing the number of qubits or the…

Quantum Physics · Physics 2023-11-28 Xia Liu , Huan Yang , Li Yang

The reliability of quantum computation critically depends on the performance of quantum error-correcting codes (QECCs). Performance of QECCs can be severely degraded by hook errors, which effectively reduce the code distance. In this work,…

Quantum Physics · Physics 2026-05-12 Harsh Gupta , Mainak Bhattacharyya , Ritik Jain , Ankur Raina

Bosonic quantum codes redundantly encode quantum information in the states of a quantum harmonic oscillator, making it possible to detect and correct errors. Schr\"odinger cat codes -- based on the superposition of two coherent states with…

Quantum Physics · Physics 2022-09-12 David S. Schlegel , Fabrizio Minganti , Vincenzo Savona

Many-body ground state preparation is an important subroutine used in the simulation of physical systems. In this paper, we introduce a flexible and efficient framework for obtaining a state preparation circuit for a large class of…

Quantum Physics · Physics 2024-11-05 Hyun-Soo Kim , Isaac H. Kim , Daniel Ranard

Fault-tolerant quantum computing (FTQC) is essential for achieving large-scale practical quantum computation. Implementing arbitrary FTQC requires the execution of a universal gate set on logical qubits, which is highly challenging.…

In this short review, I draw attention to new developments in the theory of fault tolerance in quantum computation that may give concrete direction to future work in the development of superconducting qubit systems. The basics of quantum…

Quantum Physics · Physics 2015-05-13 David P. DiVincenzo

Noise-biased qubits are a promising route toward significantly reducing the hardware overhead associated with quantum error correction. The squeezed cat code, a non-local encoding in phase space based on squeezed coherent states, is an…

Quantum Physics · Physics 2023-04-11 Timo Hillmann , Fernando Quijandría

Quantum error correction (QEC) requires the execution of deep quantum circuits with large numbers of physical qubits to protect information against errors. Designing protocols that can reduce gate and space-time overheads of QEC is…

Quantum Physics · Physics 2025-12-15 Laura Pecorari , Sven Jandura , Guido Pupillo

Preparing encoded logical states is the first step in a fault-tolerant quantum computation. Standard approaches based on concatenation or repeated measurement incur a significant time overhead. The Raussendorf-Bravyi-Harrington cluster…

Quantum Physics · Physics 2025-02-12 Thiago Bergamaschi , Yunchao Liu

We use a combination of analytical and numerical techniques to calculate the noise threshold and resource requirements for a linear optical quantum computing scheme based on parity-state encoding. Parity-state encoding is used at the lowest…

Quantum Physics · Physics 2013-05-29 A. J. F. Hayes , H. L. Haselgrove , Alexei Gilchrist , T. C. Ralph

Quantum state preparation initializes the quantum registers and is essential for running quantum algorithms. Designing state preparation circuits that entangle qubits efficiently with fewer two-qubit gates enhances accuracy and alleviates…

Quantum Physics · Physics 2024-09-04 Hanyu Wang , Daniel Bochen Tan , Jason Cong