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Multiparameter critical quantum metrology with impurity probes Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-15 George Mihailescu, Abolfazl Bayat, Steve Campbell and Andrew K Mitchell
Quantum systems can be used as probes in the context of metrology for enhanced parameter estimation. In particular, the delicacy of critical systems to perturbations can make them ideal sensors. Arguably the simplest realistic probe system is a spin- impurity, which can be manipulated and measured in-situ when embedded in a fermionic environment. Although entanglement between a single impurity probe
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Analysis of spin-squeezing generation in cavity-coupled atomic ensembles with continuous measurements Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-14 A Caprotti, M Barbiero, M G Tarallo, M G Genoni and G Bertaina
We analyze the generation of spin-squeezed states via coupling of three-level atoms to an optical cavity and continuous quantum measurement of the transmitted cavity field in order to monitor the evolution of the atomic ensemble. Using analytical treatment and microscopic simulations of the dynamics, we show that one can achieve significant spin squeezing, favorably scaling with the number of atoms
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Resource-efficient quantum principal component analysis Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-13 Youle Wang and Yu Luo
Principal component analysis (PCA) is an important dimensionality reduction method in machine learning and data analysis. Recently, the quantum version of PCA has been established to diagonalize quantum states. Although these quantum algorithms promise quantum advantages, they require substantial resources beyond the reach of state-of-the-art quantum technologies. This work aims to reduce resource
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Sequential optimal selections of single-qubit gates in parameterized quantum circuits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-12 Kaito Wada, Rudy Raymond, Yuki Sato and Hiroshi C Watanabe
In variational quantum algorithms, it is important to balance conflicting requirements of expressibility and trainability of a parameterized quantum circuit (PQC). However, appropriate PQC designs are not necessarily trivial. Here, we propose an algorithm for optimizing the PQC structure, where single-qubit gates are sequentially replaced by the optimal ones via diagonalization of a matrix whose elements
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On the relevance of weak measurements in dissipative quantum systems Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-09 Lorena Ballesteros Ferraz, John Martin, Yves Caudano
We investigate the impact of dissipation, including energy relaxation and decoherence, on weak measurements. While weak measurements have been successful in signal amplification, dissipation can compromise their usefulness. More precisely, we show that in systems with a unique steady state, weak values always converge to an expectation value of the measured observable as dissipation time tends to infinity
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Privacy-preserving quantum federated learning via gradient hiding Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-08 Changhao Li, Niraj Kumar, Zhixin Song, Shouvanik Chakrabarti, Marco Pistoia
Distributed quantum computing, particularly distributed quantum machine learning, has gained substantial prominence for its capacity to harness the collective power of distributed quantum resources, transcending the limitations of individual quantum nodes. Meanwhile, the critical concern of privacy within distributed computing protocols remains a significant challenge, particularly in standard classical
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Non-Markovian quantum gate set tomography Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-07 Ze-Tong Li, Cong-Cong Zheng, Fan-Xu Meng, Han Zeng, Tian Luan, Zai-Chen Zhang, Xu-Tao Yu
Engineering quantum devices requires reliable characterization of the quantum system, including qubits, quantum operations (also known as instruments) and the quantum noise. Recently, quantum gate set tomography (GST) has emerged as a powerful technique for self-consistently describing quantum states, gates, and measurements. However, non-Markovian correlations between the quantum system and environment
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Information flow in parameterized quantum circuits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-07 Abhinav Anand, Lasse Bjørn Kristensen, Felix Frohnert, Sukin Sim, Alán Aspuru-Guzik
In this work, we introduce a new way to quantify information flow in quantum systems, especially for parameterized quantum circuits (PQCs). We use a graph representation of the circuits and propose a new distance metric using the mutual information between gate nodes. We then present an optimization procedure for variational algorithms using paths based on the distance measure. We explore the features
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Quantum thermodynamics of boundary time-crystals Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-07 Federico Carollo, Igor Lesanovsky, Mauro Antezza, Gabriele De Chiara
Time-translation symmetry breaking is a mechanism for the emergence of non-stationary many-body phases, so-called time-crystals, in Markovian open quantum systems. Dynamical aspects of time-crystals have been extensively explored over the recent years. However, much less is known about their thermodynamic properties, also due to the intrinsic nonequilibrium nature of these phases. Here, we consider
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Quantum Fourier networks for solving parametric PDEs Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-07 Nishant Jain, Jonas Landman, Natansh Mathur, Iordanis Kerenidis
Many real-world problems, like modelling environment dynamics, physical processes, time series etc involve solving partial differential equations (PDEs) parameterised by problem-specific conditions. Recently, a deep learning architecture called Fourier neural operator (FNO) proved to be capable of learning solutions of given PDE families for any initial conditions as input. However, it results in a
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Trapping Ba+ with seven-fold enhanced efficiency utilizing an autoionizing resonance Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-03 Noah Greenberg, Brendan M White, Pei Jiang Low, Crystal Senko
Trapped ions have emerged as a front runner in quantum information processing due to their identical nature, all-to-all connectivity, and high fidelity quantum operations. As current trapped ion technologies are scaled, it will be important to improve the efficiency of loading ions, especially when working with long chains of ions or rare isotopes. Here, we compare two different isotope-selective photoionization
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Near-term distributed quantum computation using mean-field corrections and auxiliary qubits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-03 Abigail McClain Gomez, Taylor L Patti, Anima Anandkumar, Susanne F Yelin
Distributed quantum computation is often proposed to increase the scalability of quantum hardware, as it reduces cooperative noise and requisite connectivity by sharing quantum information between distant quantum devices. However, such exchange of quantum information itself poses unique engineering challenges, requiring high gate fidelity and costly non-local operations. To mitigate this, we propose
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A hybrid quantum ensemble learning model for malicious code detection Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-05-03 Qibing Xiong, Xiaodong Ding, Yangyang Fei, Xin Zhou, Qiming Du, Congcong Feng, Zheng Shan
Quantum computing as a new computing model with parallel computing capability and high information carrying capacity, has attracted a lot of attention from researchers. Ensemble learning is an effective strategy often used in machine learning to improve the performance of weak classifiers. Currently, the classification performance of quantum classifiers is not satisfactory enough due to factors such
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Operational Markovianization in randomized benchmarking Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-30 P Figueroa-Romero, M Papič, A Auer, M-H Hsieh, K Modi, I de Vega
A crucial task to obtain optimal and reliable quantum devices is to quantify their overall performance. The average fidelity of quantum gates is a particular figure of merit that can be estimated efficiently by randomized benchmarking (RB). However, the concept of gate-fidelity itself relies on the crucial assumption that noise behaves in a predictable, time-local, or so-called Markovian manner, whose
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Parameter estimation from quantum-jump data using neural networks Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-26 Enrico Rinaldi, Manuel González Lastre, Sergio García Herreros, Shahnawaz Ahmed, Maryam Khanahmadi, Franco Nori, Carlos Sánchez Muñoz
We present an inference method utilizing artificial neural networks for parameter estimation of a quantum probe monitored through a single continuous measurement. Unlike existing approaches focusing on the diffusive signals generated by continuous weak measurements, our method harnesses quantum correlations in discrete photon-counting data characterized by quantum jumps. We benchmark the precision
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Modelling non-Markovian noise in driven superconducting qubits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-26 Abhishek Agarwal, Lachlan P Lindoy, Deep Lall, François Jamet, Ivan Rungger
Non-Markovian noise can be a significant source of errors in superconducting qubits. We develop gate sequences utilising mirrored pseudoidentities that allow us to characterise and model the effects of non-Markovian noise on both idle and driven qubits. We compare three approaches to modelling the observed noise: (i) a Markovian noise model, (ii) a model including interactions with a two-level system
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An optically pumped magnetic gradiometer for the detection of human biomagnetism Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-26 Harry Cook, Yulia Bezsudnova, Lari M Koponen, Ole Jensen, Giovanni Barontini, Anna U Kowalczyk
We realise an intrinsic optically pumped magnetic gradiometer based on non-linear magneto-optical rotation. We show that our sensor can reach a gradiometric sensitivity of 18 fT cm−1Hz−1 and can reject common mode homogeneous magnetic field noise with up to 30 dB attenuation. We demonstrate that our magnetic field gradiometer is sufficiently sensitive and resilient to be employed in biomagnetic applications
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Bilayer ion trap design for 2D arrays Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-26 Gavin N Nop, Jonathan D H Smith, Daniel Stick, Durga Paudyal
Junctions are fundamental elements that support qubit locomotion in two-dimensional ion trap arrays and enhance connectivity in emerging trapped-ion quantum computers. In surface ion traps they have typically been implemented by shaping radio frequency (RF) electrodes in a single plane to minimize the disturbance to the pseudopotential. However, this method introduces issues related to RF lead routing
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Topologically protected subradiant cavity polaritons through linewidth narrowing enabled by dissipationless edge states Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-26 Yu-Wei Lu, Jing-Feng Liu, Haoxiang Jiang, Zeyang Liao
Cavity polaritons derived from strong light–matter interaction provide a basis for efficient manipulation of quantum states via cavity field. Polaritons with narrow linewidth and long lifetime are appealing in applications, such as quantum sensing and storage. Here, we propose a prototypical arrangement to implement a whispering-gallery-mode resonator with one-dimensional topological atom mirror, which
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Efficient quantum algorithm for all quantum wavelet transforms Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-21 Mohsen Bagherimehrab and Alán Aspuru-Guzik
Wavelet transforms are widely used in various fields of science and engineering as a mathematical tool with features that reveal information ignored by the Fourier transform. Unlike the Fourier transform, which is unique, a wavelet transform is specified by a sequence of numbers associated with the type of wavelet used and an order parameter specifying the length of the sequence. While the quantum
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Ten principles for responsible quantum innovation Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-21 Mauritz Kop, Mateo Aboy, Eline De Jong, Urs Gasser, Timo Minssen, I Glenn Cohen, Mark Brongersma, Teresa Quintel, Luciano Floridi and Raymond Laflamme
This paper proposes a set of guiding principles for responsible quantum innovation. The principles are organized into three functional categories: safeguarding, engaging, and advancing (SEA), and are linked to central values in responsible research and innovation (RRI). Utilizing a global equity normative framework and literature-based methodology, we connect the quantum-SEA categories to promise and
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Neural-network-designed three-qubit gates robust against charge noise and crosstalk in silicon Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-21 David W Kanaar and J P Kestner
Spin qubits in semiconductor quantum dots are a promising platform for quantum computing, however, scaling to large systems is hampered by crosstalk and charge noise. Crosstalk here refers to the unwanted off-resonant rotation of idle qubits during the resonant rotation of the target qubit. For a three-qubit system with crosstalk and charge noise, it is difficult to analytically create gate protocols
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Quantum Davidson algorithm for excited states Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-21 Nikolay V Tkachenko, Lukasz Cincio, Alexander I Boldyrev, Sergei Tretiak, Pavel A Dub and Yu Zhang
Excited state properties play a pivotal role in various chemical and physical phenomena, such as charge separation and light emission. However, the primary focus of most existing quantum algorithms has been the ground state, as seen in quantum phase estimation and the variational quantum eigensolver (VQE). Although VQE-type methods have been extended to explore excited states, these methods grapple
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Remote cross-resonance gate between superconducting fixed-frequency qubits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-25 Mari Ohfuchi, Shintaro Sato
High-fidelity quantum state transfer and remote entanglement between superconducting fixed-frequency qubits have not yet been realized. In this study, we propose an alternative remote cross-resonance gate. Considering multiple modes of a superconducting coaxial cable connecting qubits, we must find conditions under which the cross-resonance gate operates with a certain accuracy even in the presence
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Fault-tolerant fusing of repeater graph states and its application Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-11 Shuang Xu, Wei-Jiang Gong, H Z Shen and X X Yi
A repeater graph state (RGS) is a class of multipartite entangled states with favourable features for quantum communication, particularly as the enabler of all-photonic quantum repeaters. In this paper, based on an alternative formalism, we show that two RGSs can be fused via a Bell measurement in a fault-tolerant manner. The fusing of multiple RGSs can thus be carried out simultaneously and flexibly
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Pulse optimization for high-precision motional-mode characterization in trapped-ion quantum computers Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-11 Qiyao Liang, Mingyu Kang, Ming Li and Yunseong Nam
High-fidelity operation of quantum computers requires precise knowledge of the physical system through characterization. For motion-mediated entanglement generation in trapped ions, it is crucial to have precise knowledge of the motional-mode parameters such as the mode frequencies and the Lamb–Dicke parameters. Unfortunately, the state-of-the-art mode-characterization schemes do not easily render
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Optimal thermometers with spin networks Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-11 Paolo Abiuso, Paolo Andrea Erdman, Michael Ronen, Frank Noé, Géraldine Haack and Martí Perarnau-Llobet
The heat capacity of a given probe is a fundamental quantity that determines, among other properties, the maximum precision in temperature estimation. In turn, is limited by a quadratic scaling with the number of constituents of the probe, which provides a fundamental limit in quantum thermometry. Achieving this fundamental bound with realistic probes, i.e. experimentally amenable, remains an open
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Digital noise spectroscopy with a quantum sensor Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-09 Guoqing Wang (王国庆), Yuan Zhu, Boning Li, Changhao Li, Lorenza Viola, Alexandre Cooper and Paola Cappellaro
We introduce and experimentally demonstrate a quantum sensing protocol to sample and reconstruct the autocorrelation of a noise process using a single-qubit sensor under digital control modulation. This Walsh noise spectroscopy method exploits simple sequences of spin-flip pulses to generate a complete basis of digital filters that directly sample the power spectrum of the target noise in the sequency
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Optimal distributed multi-parameter estimation in noisy environments Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-08 Arne Hamann, Pavel Sekatski, Wolfgang Dür
We consider the task of multiple parameter estimation in the presence of strong correlated noise with a network of distributed sensors. The signals and the noises have different spatial dependence but are encoded with the same local generators. We study how to find and improve noise-insensitive strategies. We show that sequentially probing with GHZ states from the decoherence-free subspace that we
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Emulating two qubits with a four-level transmon qudit for variational quantum algorithms Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-08 Shuxiang Cao, Mustafa Bakr, Giulio Campanaro, Simone D Fasciati, James Wills, Deep Lall, Boris Shteynas, Vivek Chidambaram, Ivan Rungger, Peter Leek
Using quantum systems with more than two levels, or qudits, can scale the computational space of quantum processors more efficiently than using qubits, which may offer an easier physical implementation for larger Hilbert spaces. However, individual qudits may exhibit larger noise, and algorithms designed for qubits require to be recompiled to qudit algorithms for execution. In this work, we implemented
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Does entanglement enhance single-molecule pulsed biphoton spectroscopy? Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-07 Aiman Khan, Francesco Albarelli and Animesh Datta
It depends. For a single molecule interacting with one mode of a biphoton probe, we show that the spectroscopic information has three contributions, only one of which is a genuine two-photon contribution. When all the scattered light can be measured, solely this contribution exists and can be fully extracted using unentangled measurements. Furthermore, this two-photon contribution can, in principle
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Generation of stable Gaussian cluster states in optomechanical systems with multifrequency drives Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-03 Nahid Yazdi, Stefano Zippilli, David Vitali
We show how to dissipatively stabilize the quantum state of N mechanical resonators in an optomechanical system, where the resonators interact by radiation pressure with N optical modes, which are driven by properly selected multifrequency drives. We analyze the performance of this approach for the stationary preparation of Gaussian cluster states.
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Macroscopic Bell state between a millimeter-sized spin system and a superconducting qubit Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-03 Da Xu, Xu-Ke Gu, Yuan-Chao Weng, He-Kang Li, Yi-Pu Wang, Shi-Yao Zhu, J Q You
Entanglement is a fundamental property in quantum mechanics that systems share inseparable quantum correlation regardless of their mutual distances. Owing to the fundamental significance and versatile applications, the generation of quantum entanglement between macroscopic systems has been a focus of current research. Here we report on the deterministic generation and tomography of the macroscopically
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Computational capabilities and compiler development for neutral atom quantum processors—connecting tool developers and hardware experts Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-03 Ludwig Schmid, David F Locher, Manuel Rispler, Sebastian Blatt, Johannes Zeiher, Markus Müller, Robert Wille
Neutral Atom Quantum Computing (NAQC) emerges as a promising hardware platform primarily due to its long coherence times and scalability. Additionally, NAQC offers computational advantages encompassing potential long-range connectivity, native multi-qubit gate support, and the ability to physically rearrange qubits with high fidelity. However, for the successful operation of a NAQC processor, one additionally
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Unbalanced penalization: a new approach to encode inequality constraints of combinatorial problems for quantum optimization algorithms Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-02 J A Montañez-Barrera, Dennis Willsch, A Maldonado-Romo, Kristel Michielsen
Solving combinatorial optimization problems of the kind that can be codified by quadratic unconstrained binary optimization (QUBO) is a promising application of quantum computation. Some problems of this class suitable for practical applications such as the traveling salesman problem (TSP), the bin packing problem (BPP), or the knapsack problem (KP) have inequality constraints that require a particular
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Quantum secure multi-party computational geometry based on multi-party summation and multiplication Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-02 Zhao Dou, Yifei Wang, Zhaoqian Liu, Jingguo Bi, Xiubo Chen, Lixiang Li
Secure multi-party computational geometry is a branch of secure multi-party computation, which is applied in many important fields. But up to now, the research on how to solve this problem with quantum methods has just started. Therefore, we study the design of quantum secure multi-party computational geometry (QSMCG) protocols in this paper. As the foundation, we extend the two-party summation and
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Measurement-device-independent quantum random number generation over 23 Mbps with imperfect single-photon sources Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-02 You-Qi Nie, Hongyi Zhou, Bing Bai, Qi Xu, Xiongfeng Ma, Jun Zhang, Jian-Wei Pan
Quantum randomness relies heavily on the accurate characterization of the generator implementation, where the device imperfection or inaccurate characterization can lead to incorrect entropy estimation and practical bias, significantly affecting the reliability of the generated randomness. Measurement-device-independent (MDI) quantum random number generation (QRNG) endeavors to produce certified randomness
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Dissipative stability and dynamical phase transition in two driven interacting qubits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-03-26 K V Shulga
We examine a two-qubit system influenced by a time-periodic external field while interacting with a Markovian bath. This scenario significantly impacts the temporal coherence characteristics of the system. By solving the evolution equation for the density matrix operator, we determine the characteristic equilibration time and analyze the concurrence parameter-a key metric for quantifying entanglement
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Bulk-boundary correspondence in topological systems with the momentum dependent energy shift Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-03-22 Huan-Yu Wang, Zhen-Biao Yang, 0000-0002-1179-2061Wu-Ming Liu2
Bulk-boundary correspondence (BBC) remains the central topic in modern condensed matter physics and has received a boost of interest with the recent discovery of non-Hermitian skin effects. However, there still exist profound features of BBC that are beyond the existing framework. Here, we report the unexpected behavior of BBC when the Hamiltonian contains terms of the form d0(k)I , which serves as
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Near MDS and near quantum MDS codes via orthogonal arrays Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-03-22 Shanqi Pang, Chaomeng Zhang, Mengqian Chen, Miaomiao Zhang
Near maximum distance separable (NMDS) codes are closely related to interesting objects in finite geometry and have nice applications in combinatorics and cryptography. But there are many unsolved problems about construction of NMDS codes. In this paper, by using symmetrical orthogonal arrays (OAs), we construct a lot of NMDS, m-MDS and almost extremal NMDS codes. Quantum error-correcting codes (QECCs)
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Generating scalable graph states in an atom-nanophotonic interface Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-03-22 C-H Chien, S Goswami, C-C Wu, W-S Hiew, Y-C Chen, H H Jen
Scalable graph states are essential for measurement-based quantum computation and many entanglement-assisted applications in quantum technologies. Generation of these multipartite entangled states requires a controllable and efficient quantum device with delicate design of generation protocol. Here we propose to prepare high-fidelity and scalable graph states in one and two dimensions, which can be
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High flux strontium atom source Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-03-19 C-H Feng, P Robert, P Bouyer, B Canuel, J Li, S Das, C C Kwong, D Wilkowski, M Prevedelli, A Bertoldi
We present a novel cold strontium atom source designed for quantum sensors. We optimized the deceleration process to capture a large velocity class of atoms emitted from an oven and achieved a compact and low-power setup capable of generating a high atomic flux. Our approach involves velocity-dependent transverse capture of atoms using a two-dimensional magneto-optical trap. To enhance the atomic flux
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Avoiding barren plateaus in the variational determination of geometric entanglement Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-29 L Zambrano, A D Muñoz-Moller, M Muñoz, L Pereira, A Delgado
The barren plateau (BP) phenomenon is one of the main obstacles to implementing variational quantum algorithms in the current generation of quantum processors. Here, we introduce a method capable of avoiding the BP phenomenon in the variational determination of the geometric measure of entanglement for a large number of qubits. The method is based on measuring compatible two-qubit local functions whose
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Towards experimental classical verification of quantum computation Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-26 Roman Stricker, Jose Carrasco, Martin Ringbauer, Lukas Postler, Michael Meth, Claire Edmunds, Philipp Schindler, Rainer Blatt, Peter Zoller, Barbara Kraus, Thomas Monz
With today’s quantum processors venturing into regimes beyond the capabilities of classical devices, we face the challenge to verify that these devices perform as intended, even when we cannot check their results on classical computers. In a recent breakthrough in computer science, a protocol was developed that allows the verification of the output of a computation performed by an untrusted quantum
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Variational quantum algorithms for simulation of Lindblad dynamics Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-23 Tasneem M Watad, Netanel H Lindner
We introduce variational hybrid classical-quantum algorithms to simulate the Lindblad master equation and its adjoint for time-evolving Markovian open quantum systems and quantum observables. Our methods are based on a direct representation of density matrices and quantum observables as quantum superstates. We design and optimize low-depth variational quantum circuits that efficiently capture the unitary
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Experimental implementation of quantum-walk-based portfolio optimization Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-23 Dengke Qu, Edric Matwiejew, Kunkun Wang, Jingbo Wang, Peng Xue
The application of quantum algorithms has attracted much attention as it holds the promise of solving practical problems that are intractable to classical algorithms. One such application is the recent development of a quantum-walk-based optimization algorithm approach to portfolio optimization under the modern portfolio theory framework. In this paper, we demonstrate an experimental realization of
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Fast generation of spin squeezing via resonant spin-boson coupling Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-21 Diego Barberena, Sean R Muleady, John J Bollinger, Robert J Lewis-Swan, Ana Maria Rey
We propose protocols for the creation of useful entangled states in a system of spins collectively coupled to a bosonic mode, directly applicable to trapped-ion and cavity QED setups. The protocols use coherent manipulations of the resonant spin-boson interactions naturally arising in these systems to prepare spin squeezed states exponentially fast in time. The resonance condition harnesses the full
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Hybrid actor-critic algorithm for quantum reinforcement learning at CERN beam lines Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-21 Michael Schenk, Elías F Combarro, Michele Grossi, Verena Kain, Kevin Shing Bruce Li, Mircea-Marian Popa, Sofia Vallecorsa
Free energy-based reinforcement learning (FERL) with clamped quantum Boltzmann machines (QBM) was shown to significantly improve the learning efficiency compared to classical Q-learning with the restriction, however, to discrete state-action space environments. In this paper, the FERL approach is extended to multi-dimensional continuous state-action space environments to open the doors for a broader
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A thermodynamic approach to optimization in complex quantum systems Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-16 Alberto Imparato, Nicholas Chancellor, Gabriele De Chiara
We consider the problem of finding the energy minimum of a complex quantum Hamiltonian by employing a non-Markovian bath prepared in a low energy state. The energy minimization problem is thus turned into a thermodynamic cooling protocol in which we repeatedly put the system of interest in contact with a colder auxiliary system. By tuning the internal parameters of the bath, we show that the optimal
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An expressive ansatz for low-depth quantum approximate optimisation Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-13 V Vijendran, Aritra Das, Dax Enshan Koh, Syed M Assad, Ping Koy Lam
The quantum approximate optimisation algorithm (QAOA) is a hybrid quantum–classical algorithm used to approximately solve combinatorial optimisation problems. It involves multiple iterations of a parameterised ansatz that consists of a problem and mixer Hamiltonian, with the parameters being classically optimised. While QAOA can be implemented on near-term quantum hardware, physical limitations such
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Compilation of algorithm-specific graph states for quantum circuits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-12 Madhav Krishnan Vijayan, Alexandru Paler, Jason Gavriel, Casey R Myers, Peter P Rohde, Simon J Devitt
We present a quantum circuit compiler that prepares an algorithm-specific graph state from quantum circuits described in high level languages, such as Cirq and Q#. The computation can then be implemented using a series of non-Pauli measurements on this graph state. By compiling the graph state directly instead of starting with a standard lattice cluster state and preparing it over the course of the
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Excitons guided by polaritons Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-12 K Mukherjee, S Wüster
We show that an exciton on a discrete chain of sites can be guided by effective measurements induced by an ambient, non-equilibrium medium that is synchronised to the exciton transport. For experimental verification, we propose a hybrid cold atom platform, carrying the exciton as electronic excitation on a chain of atoms, which are surrounded by a slow light medium supporting polaritons. The chain
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Low-complexity adaptive reconciliation protocol for continuous-variable quantum key distribution Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-08 Xue-Qin Jiang, Shengyuan Xue, Jiahao Tang, Peng Huang, Guihua Zeng
In continuous-variable quantum key distribution systems, reconciliation is a crucial step that significantly affects the secret key rate (SKR). The rateless protocol based on Raptor codes can achieve high reconciliation efficiency at low signal-to-noise ratios (SNRs). However, the high complexity of low-density parity-check (LDPC) codes used for the precoding in Raptor codes limits the speed of reconciliation
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Optimizing for periodicity: a model-independent approach to flux crosstalk calibration for superconducting circuits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-02 X Dai, R Trappen, R Yang, S M Disseler, J I Basham, J Gibson, A J Melville, B M Niedzielski, R Das, D K Kim, J L Yoder, S J Weber, C F Hirjibehedin, D A Lidar, A Lupascu
Flux tunability is an important engineering resource for superconducting circuits. Large-scale quantum computers based on flux-tunable superconducting circuits face the problem of flux crosstalk, which needs to be accurately calibrated to realize high-fidelity quantum operations. Typical calibration methods either assume that circuit elements can be effectively decoupled and simple models can be applied
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Wafer-scale uniformity of Dolan-bridge and bridgeless Manhattan-style Josephson junctions for superconducting quantum processors Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-02-02 Nandini Muthusubramanian, Matvey Finkel, Pim Duivestein, Christos Zachariadis, Sean L M van der Meer, Hendrik M Veen, Marc W Beekman, Thijs Stavenga, Alessandro Bruno, Leonardo DiCarlo
We investigate die-level and wafer-scale uniformity of Dolan-bridge and bridgeless Manhattan-style Josephson junctions, using multiple substrates with and without through-silicon vias (TSVs). Dolan junctions fabricated on planar substrates have the highest yield and lowest room-temperature conductance spread, equivalent to ∼100MHz in transmon frequency. In TSV-integrated substrates, Dolan junctions
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Efficient quantum simulation of nonlinear interactions using SNAP and Rabi gates Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-01-30 Kimin Park, Petr Marek, Radim Filip
Quantum simulations provide means to probe challenging problems within controllable quantum systems. However, implementing or simulating deep-strong nonlinear couplings between bosonic oscillators on physical platforms remains a challenge. We present a deterministic simulation technique that efficiently and accurately models nonlinear bosonic dynamics. This technique alternates between tunable Rabi
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Computing electronic correlation energies using linear depth quantum circuits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-01-29 Chong Hian Chee, Adrian M Mak, Daniel Leykam, Panagiotis Kl Barkoutsos, Dimitris G Angelakis
Efficient computation of molecular energies is an exciting application of quantum computing for quantum chemistry, but current noisy intermediate-scale quantum (NISQ) devices can only execute shallow circuits, limiting existing variational quantum algorithms, which require deep entangling quantum circuit ansatzes to capture correlations, to small molecules. Here we demonstrate a variational NISQ-friendly
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Generation and characterization of polarization-entangled states using quantum dot single-photon sources Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-01-22 Mauro Valeri, Paolo Barigelli, Beatrice Polacchi, Giovanni Rodari, Gianluca De Santis, Taira Giordani, Gonzalo Carvacho, Nicolò Spagnolo, Fabio Sciarrino
Single-photon sources based on semiconductor quantum dots find several applications in quantum information processing due to their high single-photon indistinguishability, on-demand generation, and low multiphoton emission. In this context, the generation of entangled photons represents a challenging task with a possible solution relying on the interference in probabilistic gates of identical photons
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Experimentally ruling out joint reality based on operational completeness Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-01-19 Qiuxin Zhang, Yu Xiang, Xiaoting Gao, Chenhao Zhu, Yuxin Wang, Liangyu Ding, Xiang Zhang, Shuaining Zhang, Shuming Cheng, Michael J W Hall, Qiongyi He, Wei Zhang
Whether the observables of a physical system admit real values is of fundamental importance to a deep understanding of nature. In this work, we report a device-independent experiment to confirm that the joint reality of two observables on a single two-level system is incompatible with the assumption of operational completeness, which is strictly weaker than that of preparation noncontextuality. We
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Comment on ‘From counterportation to local wormholes’ Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-01-04 Justin Dressel, Gregory Reznik, Lev Vaidman
Hatim Salih discovered a method for transferring a quantum state with no particles present in the transmission channel, which he named counterportation. Recently (Salih 2023 Quantum Sci. Technol. 8 025016), he presented a feasible procedure for its implementation. The modification of the protocol by Aharonov and Vaidman, adopted by Salih, justifies the claim that no photons were present in the transmission