Computing $n$-time correlation functions without ancilla qubits

• URL: http://arxiv.org/abs/2504.12975v2
• Date: Mon, 07 Jul 2025 08:36:27 GMT
• Title: Computing $n$-time correlation functions without ancilla qubits
• Authors: Xiaoyang Wang, Long Xiong, Xiaoxia Cai, Xiao Yuan,
• Abstract summary: We introduce a method to compute $n$-time correlation functions using only unitary evolutions on the system of interest.<n>This approach substantially relaxes hardware connectivity requirements for digital processors.<n>We demonstrate our protocol on IBM quantum hardware up to 12 qubits to measure the single-particle spectrum of the Schwinger model.
• Score: 3.5557611808487644
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: The $n$-time correlation function is pivotal for establishing connections between theoretical predictions and experimental observations of a quantum system. Conventional methods for computing $n$-time correlation functions on quantum computers, such as the Hadamard test, generally require an ancilla qubit that controls the entire system -- an approach that poses challenges for digital quantum devices with limited qubit connectivity, as well as for analog quantum platforms lacking controlled operations. Here, we introduce a method to compute $n$-time correlation functions using only unitary evolutions on the system of interest, thereby eliminating the need for ancillas and the control operations. This approach substantially relaxes hardware connectivity requirements for digital processors and enables more practical measurements of $n$-time correlation functions on analog platforms. We demonstrate our protocol on IBM quantum hardware up to 12 qubits to measure the single-particle spectrum of the Schwinger model and the out-of-time-order correlator in the transverse-field Ising model. In the demonstration, we further introduce an error mitigation procedure based on signal processing that integrates signal filtering and correlation analysis, and successfully reproduces the noiseless simulation results from the noisy hardware. Our work highlights a route to exploring complex quantum many-body correlation functions in practice, even in the presence of realistic hardware limitations and noise.

Related papers

• Quantum error mitigation in optimized circuits for particle-density correlations in real-time dynamics of the Schwinger model [0.0]
  In principle, it is possible to calculate non-equal-time correlation functions, from which one can detect interesting phenomena.<n>In practice, these calculations are strongly affected by noise, due to the complexity of the required quantum circuits.<n>We derive a digital circuit implementation of the time-evolution of particle-density correlation operators and their correlation, comparing results from exact evolution, bare noisy simulations and simulations with different error mitigation techniques.
  arXiv  Detail & Related papers  (2025-01-18T17:32:59Z)
• A learning agent-based approach to the characterization of open quantum systems [0.0]
  We introduce the open Quantum Model Learning Agent (oQMLA) framework to account for Markovian noise through the Liouvillian formalism.<n>By simultaneously learning the Hamiltonian and jump operators, oQMLA independently captures both the coherent and incoherent dynamics of a system.<n>We validate our implementation in simulated scenarios of increasing complexity, demonstrating its robustness to hardware-induced measurement errors.
  arXiv  Detail & Related papers  (2025-01-09T16:25:17Z)
• Dissipation-induced Quantum Homogenization for Temporal Information Processing [44.99833362998488]
  Quantum reservoirs have great potential as they utilize the complex real-time dissipative dynamics of quantum systems for information processing and target time-series generation without precise control or fine-tuning of the Hamiltonian parameters.<n>We propose the disordered quantum homogenizer as an alternative platform, and prove it satisfies the necessary and sufficient conditions - stability and contractivity - of the reservoir dynamics.<n>The results indicate that the quantum homogenization protocol, physically implementable as either nuclear magnetic resonance ensemble or a photonic system, can potentially function as a reservoir computer.
  arXiv  Detail & Related papers  (2024-12-13T09:05:41Z)
• Efficient Learning for Linear Properties of Bounded-Gate Quantum Circuits [63.733312560668274]
  Given a quantum circuit containing d tunable RZ gates and G-d Clifford gates, can a learner perform purely classical inference to efficiently predict its linear properties? We prove that the sample complexity scaling linearly in d is necessary and sufficient to achieve a small prediction error, while the corresponding computational complexity may scale exponentially in d. We devise a kernel-based learning model capable of trading off prediction error and computational complexity, transitioning from exponential to scaling in many practical settings.
  arXiv  Detail & Related papers  (2024-08-22T08:21:28Z)
• Syncopated Dynamical Decoupling for Suppressing Crosstalk in Quantum Circuits [12.29963230632145]
  We study the use of dynamical decoupling in characterizing undesired two-qubit couplings and the underlying single-qubit decoherence. We develop a syncopated decoupling technique which protects against decoherence and selectively targets unwanted two-qubit interactions.
  arXiv  Detail & Related papers  (2024-03-12T17:18:35Z)
• System Characterization of Dispersive Readout in Superconducting Qubits [37.940693612514984]
  We introduce a single protocol to measure the dispersive shift, resonator linewidth, and drive power used in the dispersive readout of superconducting qubits. We find that the resonator linewidth is poorly controlled with a factor of 2 between the maximum and minimum measured values. We also introduce a protocol for measuring the readout system efficiency using the same power levels as are used in typical qubit readout.
  arXiv  Detail & Related papers  (2024-02-01T08:15:16Z)
• Mitigating crosstalk errors by randomized compiling: Simulation of the BCS model on a superconducting quantum computer [41.94295877935867]
  Crosstalk errors, stemming from CNOT two-qubit gates, are a crucial source of errors on numerous quantum computing platforms. We develop and apply an extension of the randomized compiling protocol that includes a special treatment of neighboring qubits. Our twirling of neighboring qubits is shown to dramatically improve the noise estimation protocol without the need to add new qubits or circuits.
  arXiv  Detail & Related papers  (2023-05-03T18:00:02Z)
• Optimal quantum control via genetic algorithms for quantum state engineering in driven-resonator mediated networks [68.8204255655161]
  We employ a machine learning-enabled approach to quantum state engineering based on evolutionary algorithms. We consider a network of qubits -- encoded in the states of artificial atoms with no direct coupling -- interacting via a common single-mode driven microwave resonator. We observe high quantum fidelities and resilience to noise, despite the algorithm being trained in the ideal noise-free setting.
  arXiv  Detail & Related papers  (2022-06-29T14:34:00Z)
• Efficient and robust estimation of many-qubit Hamiltonians [0.0]
  Characterizing the interactions and dynamics of quantum mechanical systems is an essential task in development of quantum technologies. We propose an efficient protocol for characterizing the underlying Hamiltonian dynamics and the noise of a multi-qubit device. This protocol can be used to parallelize to learn the Hamiltonian, rendering it applicable for the characterization of both current and future quantum devices.
  arXiv  Detail & Related papers  (2022-05-19T13:52:32Z)
• Robust measurements of $n$-point correlation functions of driven-dissipative quantum systems on a digital quantum computer [0.0]
  We propose and demonstrate a unified hierarchical method to measure correlation functions. The time evolution of the system is repeatedly interrupted by interacting an ancilla qubit with the system. We implement the method on a quantum computer in order to measure single-particle Green's functions of a driven-dissipative fermionic system.
  arXiv  Detail & Related papers  (2022-04-26T15:57:22Z)
• Interactive Protocols for Classically-Verifiable Quantum Advantage [46.093185827838035]
  "Interactions" between a prover and a verifier can bridge the gap between verifiability and implementation. We demonstrate the first implementation of an interactive quantum advantage protocol, using an ion trap quantum computer.
  arXiv  Detail & Related papers  (2021-12-09T19:00:00Z)
• Quantum Causal Unravelling [44.356294905844834]
  We develop the first efficient method for unravelling the causal structure of the interactions in a multipartite quantum process. Our algorithms can be used to identify processes that can be characterized efficiently with the technique of quantum process tomography.
  arXiv  Detail & Related papers  (2021-09-27T16:28:06Z)
• Suppression of crosstalk in superconducting qubits using dynamical decoupling [0.0]
  Super superconducting quantum processors with interconnected transmon qubits are noisy and prone to various errors. ZZ-coupling between qubits in fixed frequency transmon architectures is always present and contributes to both coherent and incoherent crosstalk errors. We propose the use of dynamical decoupling to suppress the crosstalk, and demonstrate the success of this scheme through experiments on several IBM quantum cloud processors.
  arXiv  Detail & Related papers  (2021-08-10T09:16:05Z)
• Accurate methods for the analysis of strong-drive effects in parametric gates [94.70553167084388]
  We show how to efficiently extract gate parameters using exact numerics and a perturbative analytical approach. We identify optimal regimes of operation for different types of gates including $i$SWAP, controlled-Z, and CNOT.
  arXiv  Detail & Related papers  (2021-07-06T02:02:54Z)
• Quantum Markov Chain Monte Carlo with Digital Dissipative Dynamics on Quantum Computers [52.77024349608834]
  We develop a digital quantum algorithm that simulates interaction with an environment using a small number of ancilla qubits. We evaluate the algorithm by simulating thermal states of the transverse Ising model.
  arXiv  Detail & Related papers  (2021-03-04T18:21:00Z)
• Probing quantum information propagation with out-of-time-ordered correlators [41.12790913835594]
  Small-scale quantum information processors hold the promise to efficiently emulate many-body quantum systems. Here, we demonstrate the measurement of out-of-time-ordered correlators (OTOCs) A central requirement for our experiments is the ability to coherently reverse time evolution.
  arXiv  Detail & Related papers  (2021-02-23T15:29:08Z)
• Information Scrambling in Computationally Complex Quantum Circuits [56.22772134614514]
  We experimentally investigate the dynamics of quantum scrambling on a 53-qubit quantum processor. We show that while operator spreading is captured by an efficient classical model, operator entanglement requires exponentially scaled computational resources to simulate.
  arXiv  Detail & Related papers  (2021-01-21T22:18:49Z)
• Preparation of excited states for nuclear dynamics on a quantum computer [117.44028458220427]
  We study two different methods to prepare excited states on a quantum computer. We benchmark these techniques on emulated and real quantum devices. These findings show that quantum techniques designed to achieve good scaling on fault tolerant devices might also provide practical benefits on devices with limited connectivity and gate fidelity.
  arXiv  Detail & Related papers  (2020-09-28T17:21:25Z)

This list is automatically generated from the titles and abstracts of the papers in this site.

This site does not guarantee the quality of this site (including all information) and is not responsible for any consequences.