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- Experimental realization of active nonlinear feedback control from hot
rubidium vapor-
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Authors: Xiaozhou Pan; Tianxiang Wei, Kai Zhang Jietai Jing
First page: 045020
Abstract: Feedback control plays a crucial role in preparation and manipulation of quantum states, to evolve the quantum system towards a desired result. Here we report a novel feedback control system utilizing two four-wave mixing (FWM) processes, in which the first FWM process functions as an amplifier while the second FWM process serves as an active nonlinear controller. We experimentally investigate the classical properties of the output states, and demonstrate the manipulation of quantum states through the active nonlinear controller. Remarkably, we observe that the quantum correlation of the quantum states can be efficiently controlled and enhanced, even when the amplifier operates at a significantly low level of pump power. Furthermore, we identify an optimal intensity gain for the active nonlinear controller, which maximizes the quantum correlation of the system. These findings present a new strategy employing an active controller to enhance quantum correlation, which holds the potential to improve the communication fidelity of quantum information processing and enhance the measurement precision of quantum metrology in future applications.
Citation: Quantum Science and Technology
PubDate: 2024-08-01T23:00:00Z
DOI: 10.1088/2058-9565/ad617f
Issue No: Vol. 9, No. 4 (2024)
- Distributing circuits over heterogeneous, modular quantum computing
network architectures-
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Authors: Pablo Andres-Martinez; Tim Forrer, Daniel Mills, Jun-Yi Wu, Luciana Henaut, Kentaro Yamamoto, Mio Murao Ross Duncan
First page: 045021
Abstract: We consider a heterogeneous network of quantum computing modules, sparsely connected via Bell states. Operations across these connections constitute a computational bottleneck and they are likely to add more noise to the computation than operations performed within a module. We introduce several techniques for transforming a given quantum circuit into one implementable on such a network, minimising the number of Bell states required to do so. We extend previous works on circuit distribution to the case of heterogeneous networks. On the one hand, we extend the hypergraph approach of Andres-Martinez and Heunen (2019 Phys. Rev. A 100 032308) to arbitrary network topologies, and we propose the use of Steiner trees to detect and reuse common connections, further reducing the cost of entanglement sharing within the network. On the other hand, we extend the embedding techniques of Wu et al (2023 Quantum7 1196) to networks with more than two modules. We show that, with careful manipulation of trade-offs, these two new approaches can be combined into a single automated framework. Our proposal is implemented and benchmarked; the results confirm that our contributions make noticeable improvements upon the aforementioned works and complement their weaknesses.
Citation: Quantum Science and Technology
PubDate: 2024-08-05T23:00:00Z
DOI: 10.1088/2058-9565/ad6734
Issue No: Vol. 9, No. 4 (2024)
- Bang-bang optimal control in coherent spin dynamics of radical pairs in
quantum biology-
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Authors: Ugur G Abdulla; Jose Rodrigues, Pablo Jimenez, Chenming Zhen Carlos Martino
First page: 045022
Abstract: Optimal control of the external electromagnetic field input for the maximization of the quantum triplet-singlet yield of the radical pairs in biochemical reactions modeled by Schrödinger system with spin Hamiltonians given by the sum of Zeeman interaction and hyperfine coupling interaction terms are analyzed. Fréchet differentiability and Pontryagin Maximum Principle in Hilbert space is proved and the bang-bang structure of the optimal control is established. A closed optimality system of nonlinear differential equations for the identification of the bang-bang optimal control is revealed. Numerical methods for the identification of the bang-bang optimal control based on the Pontryagin maximum principle are developed. Numerical simulations are pursued, and the convergence and stability of the numerical methods are demonstrated. The results contribute towards understanding the structure-function relationship of the putative magnetoreceptor to manipulate and enhance quantum coherences at room temperature and leveraging biofidelic function to inspire novel quantum devices.
Citation: Quantum Science and Technology
PubDate: 2024-08-07T23:00:00Z
DOI: 10.1088/2058-9565/ad68a1
Issue No: Vol. 9, No. 4 (2024)
- Ratchet loading and multi-ensemble operation in an optical lattice clock
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Authors: Youssef S Hassan; Takumi Kobayashi, Tobias Bothwell, Jacob L Seigel, Benjamin D Hunt, Kyle Beloy, Kurt Gibble, Tanner Grogan Andrew D Ludlow
First page: 045023
Abstract: We demonstrate programmable control over the spatial distribution of ultra-cold atoms confined in an optical lattice. The control is facilitated through a combination of spatial manipulation of the magneto-optical trap and atomic population shelving to a metastable state. We first employ the technique to load an extended (5 mm) atomic sample with uniform density in an optical lattice clock (OLC), reducing atomic interactions and realizing remarkable frequency homogeneity across the atomic cloud. We also prepare multiple spatially separated atomic ensembles, and realize multi-ensemble clock operation within the standard one-dimensional (1D) OLC architecture. Leveraging this technique, we prepare two oppositely spin-polarized ensembles that are independently addressable, offering a platform for implementing spectroscopic protocols for enhanced tracking of local oscillator phase. Finally, we demonstrate a relative fractional frequency instability at one second of between two ensembles, useful for characterization of intra-lattice differential systematics.
Citation: Quantum Science and Technology
PubDate: 2024-08-07T23:00:00Z
DOI: 10.1088/2058-9565/ad6286
Issue No: Vol. 9, No. 4 (2024)
- Optimal and robust quantum state tomography of star-topology register
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Authors: Ran Liu; Yanjun Hou, Ze Wu, Hui Zhou, Jiahui Chen, Zhaokai Li Xinhua Peng
First page: 045024
Abstract: While quantum state tomography plays a vital role in the verification and benchmarking of quantum systems, it is an intractable task if the controllability of the quantum registers is constrained. In this paper, we propose a novel scheme for optimal and robust quantum state tomography for systems with constrained controllability. Based on the specific symmetry, we decompose the Hilbert space to alleviate the complexity of tomography and design a compact strategy with the minimum number of measurements. To switch between these measurement settings, we adopted parameterized quantum circuits consisting of local operations and free evolution, which are easy to implement in most practical systems. Then the parameters of these circuits were optimized to improve the robustness against errors of measurements. We demonstrated the experimental feasibility of our method on a 4-spin star-topology register and numerically studied its ability to characterize large-scale systems on a 10-spin star-topology register, respectively. Our results can help future investigations of quantum systems with constrained ability of quantum control and measurement.
Citation: Quantum Science and Technology
PubDate: 2024-08-07T23:00:00Z
DOI: 10.1088/2058-9565/ad692c
Issue No: Vol. 9, No. 4 (2024)
- A square-root speedup for finding the smallest eigenvalue
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Authors: Alex Kerzner; Vlad Gheorghiu, Michele Mosca, Thomas Guilbaud, Federico Carminati, Fabio Fracas Luca Dellantonio
First page: 045025
Abstract: We describe a quantum algorithm for finding the smallest eigenvalue of a Hermitian matrix. This algorithm combines quantum phase estimation and quantum amplitude estimation to achieve a quadratic speedup with respect to the best classical algorithm in terms of matrix dimensionality, i.e. 9black-box queries to an oracle encoding the matrix, where N is the matrix dimension and ɛ is the desired precision. In contrast, the best classical algorithm for the same task requires queries. In addition, this algorithm allows the user to select any constant success probability. We also provide a similar algorithm with the same runtime that allows us to prepare a quantum state lying mostly in the matrix’s low-energy subspace. We implement simulations of both algorithms and demonstrate their application to problems in quantum chemistry and materials science.
Citation: Quantum Science and Technology
PubDate: 2024-08-11T23:00:00Z
DOI: 10.1088/2058-9565/ad6a36
Issue No: Vol. 9, No. 4 (2024)
- A differentiable quantum phase estimation algorithm
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Authors: Davide Castaldo; Soran Jahangiri, Agostino Migliore, Juan Miguel Arrazola Stefano Corni
First page: 045026
Abstract: The simulation of electronic properties is a pivotal issue in modern electronic structure theory, driving significant efforts over the past decades to develop protocols for computing energy derivatives. In this work, we address this problem by developing a strategy to integrate the quantum phase estimation algorithm within a fully differentiable framework. This is accomplished by devising a smooth estimator able to tackle arbitrary initial states. We provide analytical expressions to characterize the statistics and algorithmic cost of this estimator. Furthermore, we provide numerical evidence that the estimation accuracy is retained when an arbitrary state is considered and that it exceeds the one of standard majority rule. We explicitly use this procedure to estimate chemically relevant quantities, demonstrating our approach through ground-state and triplet excited state geometry optimization with simulations involving up to 19 qubits. This work paves the way for new quantum algorithms that combine interference methods and quantum differentiable programming.
Citation: Quantum Science and Technology
PubDate: 2024-08-12T23:00:00Z
DOI: 10.1088/2058-9565/ad69bc
Issue No: Vol. 9, No. 4 (2024)
- Entanglement-preserving measurement of the Bell parameter on a single
entangled pair-
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Authors: Salvatore Virzì; Enrico Rebufello, Francesco Atzori, Alessio Avella, Fabrizio Piacentini, Rudi Lussana, Iris Cusini, Francesca Madonini, Federica Villa, Marco Gramegna, Eliahu Cohen, Ivo Pietro Degiovanni Marco Genovese
First page: 045027
Abstract: Bell inequalities represent one of the cornerstones of quantum foundations, and a fundamental tool for quantum technologies. Although a lot of effort was put in exploring and generalizing them, because of the wave function collapse it was deemed impossible to estimate the entire Bell parameter from one entangled pair, since this would involve measuring incompatible observables on the same quantum state. Conversely, here it is reported the first implementation of a new generation of Bell inequality tests, able to extract a Bell parameter value from each entangled pair and, at the same time, preserve the pair entanglement instead of destroying it. This is obtained by exploiting sequences of weak measurements, allowing incompatible observable measurements on a quantum state without collapsing its wave function. On the fundamental side, by removing the need to choose between different measurement bases our approach stretches the concept of counterfactual definiteness, since it allows measuring the entangled pair in all the bases needed for the Bell inequality test, intrinsically eliminating the issues connected with the otherwise not-chosen bases. On the practical side, after our Bell parameter measurement the entanglement within the pair remains (basically) unaltered, hence exploitable for other quantum-technology-related or foundational purposes.
Citation: Quantum Science and Technology
PubDate: 2024-08-19T23:00:00Z
DOI: 10.1088/2058-9565/ad6a37
Issue No: Vol. 9, No. 4 (2024)
- Photonic variational quantum eigensolver using entanglement measurements
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Authors: Jinil Lee; Wooyeong Song, Donghwa Lee, Yosep Kim, Seung-Woo Lee, Hyang-Tag Lim, Hojoong Jung, Sang-Wook Han Yong-Su Kim
First page: 045028
Abstract: Variational quantum eigensolver (VQE), which combines quantum systems with classical computational power, has been arisen as a promising candidate for near-term quantum computing applications. However, the experimental resources such as the number of measurements to implement VQE rapidly increases as the Hamiltonian problem size grows. Applying entanglement measurements to reduce the number of measurement setups has been proposed to address this issue, but, entanglement measurements themselves can introduce additional resource demands. Here, we apply entanglement measurements to the photonic VQE utilizing polarization and path degrees of freedom of a single-photon. In our photonic VQE, entanglement measurements can be deterministically implemented using linear optics, so it takes full advantage of introducing entanglement measurements without additional experimental demands. Moreover, we show that such a setup can mitigate errors in measurement apparatus for a certain Hamiltonian.
Citation: Quantum Science and Technology
PubDate: 2024-08-20T23:00:00Z
DOI: 10.1088/2058-9565/ad6d87
Issue No: Vol. 9, No. 4 (2024)
- Thermodynamic sensing of quantum nonlinear noise correlations
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Authors: Nilakantha Meher; Tomáš Opatrný Gershon Kurizki
First page: 045029
Abstract: We put forth the concept of quantum noise sensing in nonlinear two-mode interferometers coupled to mechanical oscillators. These autonomous machines are capable of sensing quantum nonlinear correlations of two-mode noisy fields via their thermodynamic variable of extractable work, alias work capacity (WC) or ergotropy. The fields are formed by thermal noise input via its interaction with multi-level systems inside the interferometer. Such interactions amount to the generation of two-mode quantum nonlinear gauge fields that may be partly unknown. We show that by monitoring a mechanical oscillator coupled to the interferometer, one can sense the WC of one of the output field modes and thereby reveal the quantum nonlinear correlations of the field. The proposed quantum sensing method can provide an alternative to quantum multiport interferometry where the output field is unraveled by tomography. This method may advance the simulation and control of multimode quantum nonlinear gauge fields.
Citation: Quantum Science and Technology
PubDate: 2024-08-21T23:00:00Z
DOI: 10.1088/2058-9565/ad6eb4
Issue No: Vol. 9, No. 4 (2024)
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