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Parameter estimation from quantum-jump data using neural networks Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-25 Enrico Rinaldi, Manuel González Lastre, Sergio García Herreros, Shahnawaz Ahmed, Maryam Khanahmadi, Franco Nori and 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 : 2024-04-25 Abhishek Agarwal, Lachlan P Lindoy, Deep Lall, François Jamet and 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 : 2024-04-25 Harry Cook, Yulia Bezsudnova, Lari M Koponen, Ole Jensen, Giovanni Barontini and 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 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 : 2024-04-25 Gavin N Nop, Jonathan D H Smith, Daniel Stick and 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 : 2024-04-25 Yu-Wei Lu, Jing-Feng Liu, Haoxiang Jiang and 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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Remote cross-resonance gate between superconducting fixed-frequency qubits Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-04-24 Mari Ohfuchi and 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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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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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
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Indistinguishability-assisted two-qubit entanglement distillation Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-01-04 Farzam Nosrati, Bruno Bellomo, Gabriele De Chiara, Giuseppe Compagno, Roberto Morandotti, Rosario Lo Franco
Production of quantum states exhibiting a high degree of entanglement out of noisy conditions is one of the main goals of quantum information science. Here, we provide a conditional yet efficient entanglement distillation method which functions within the framework of spatially localized operations and classical communication. This method exploits indistinguishability effects due to the spatial overlap
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Quantum circuits for measuring weak values, Kirkwood–Dirac quasiprobability distributions, and state spectra Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-01-04 Rafael Wagner, Zohar Schwartzman-Nowik, Ismael L Paiva, Amit Te’eni, Antonio Ruiz-Molero, Rui Soares Barbosa, Eliahu Cohen, Ernesto F Galvão
Weak values and Kirkwood–Dirac (KD) quasiprobability distributions have been independently associated with both foundational issues in quantum theory and advantages in quantum metrology. We propose simple quantum circuits to measure weak values, KD distributions, and spectra of density matrices without the need for post-selection. This is achieved by measuring unitary-invariant, relational properties
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Building spatial symmetries into parameterized quantum circuits for faster training Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-01-04 Frédéric Sauvage, Martín Larocca, Patrick J Coles, M Cerezo
Practical success of quantum learning models hinges on having a suitable structure for the parameterized quantum circuit. Such structure is defined both by the types of gates employed and by the correlations of their parameters. While much research has been devoted to devising adequate gate-sets, typically respecting some symmetries of the problem, very little is known about how their parameters should
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Amplitude amplification-inspired QAOA: improving the success probability for solving 3SAT Quantum Sci. Technol. (IF 6.7) Pub Date : 2024-01-04 Alexander Mandl, Johanna Barzen, Marvin Bechtold, Frank Leymann, Karoline Wild
The Boolean satisfiability problem (SAT), in particular 3SAT with its bounded clause size, is a well-studied problem since a wide range of decision problems can be reduced to it. The Quantum Approximate Optimization Algorithm (QAOA) is a promising candidate for solving 3SAT for Noisy Intermediate-Scale Quantum devices in the near future due to its simple quantum ansatz. However, although QAOA generally
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Extending the variational quantum eigensolver to finite temperatures Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-12-22 Johannes Selisko, Maximilian Amsler, Thomas Hammerschmidt, Ralf Drautz, Thomas Eckl
We present a variational quantum thermalizer (VQT), called quantum-VQT (qVQT), which extends the variational quantum eigensolver to finite temperatures. The qVQT makes use of an intermediate measurement between two variational circuits to encode a density matrix on a quantum device. A classical optimization provides the thermal state and, simultaneously, all associated excited states of a quantum mechanical
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Security of quantum key distribution with imperfect phase randomisation Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-12-22 Guillermo Currás-Lorenzo, Shlok Nahar, Norbert Lütkenhaus, Kiyoshi Tamaki, Marcos Curty
The performance of quantum key distribution (QKD) is severely limited by multiphoton emissions, due to the photon-number-splitting attack. The most efficient solution, the decoy-state method, requires that the phases of all transmitted pulses are independent and uniformly random. In practice, however, these phases are often correlated, especially in high-speed systems, which opens a security loophole
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On readout and initialisation fidelity by finite demolition single shot readout Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-12-19 Majid Zahedian, Max Keller, Minsik Kwon, Javid Javadzade, Jonas Meinel, Vadim Vorobyov, Jörg Wrachtrup
Ideal projective quantum measurement makes the system state collapse in one of the observable operator eigenstates |ϕα⟩ , making it a powerful tool for preparing the system in the desired pure state. Nevertheless, experimental realisations of projective measurement are not ideal. During the measurement time needed to overcome the classical noise of the apparatus, the system state is often (slightly)
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Quantum optical induced-coherence tomography by a hybrid interferometer Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-12-19 Eun Mi Kim, Sun Kyung Lee, Sang Min Lee, Myeong Soo Kang, Hee Su Park
Quantum interferometry based on induced-coherence phenomena has demonstrated the possibility of undetected-photon measurements. Perturbation in the optical path of probe photons can be detected by interference signals generated by quantum mechanically correlated twin photons propagating through a different path, possibly at a different wavelength. To the best of our knowledge, this work demonstrates
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Quantum-classical hybrid neural networks in the neural tangent kernel regime Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-12-18 Kouhei Nakaji, Hiroyuki Tezuka, Naoki Yamamoto
Recently, quantum neural networks or quantum–classical neural networks (qcNN) have been actively studied, as a possible alternative to the conventional classical neural network (cNN), but their practical and theoretically-guaranteed performance is still to be investigated. In contrast, cNNs and especially deep cNNs, have acquired several solid theoretical basis; one of those basis is the neural tangent
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Certification of non-Gaussian Einstein–Podolsky–Rosen steering Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-12-14 Mingsheng Tian, Zihang Zou, Da Zhang, David Barral, Kamel Bencheikh, Qiongyi He, Feng-Xiao Sun, Yu Xiang
Non-Gaussian quantum states are a known necessary resource for reaching a quantum advantage and for violating Bell inequalities in continuous variable systems. As one kind of manifestation of quantum correlations, Einstein–Podolsky–Rosen steering enables verification of shared entanglement even when one of the subsystems is not characterized. However, how to detect and classify such an effect for non-Gaussian
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Large-alphabet time-bin quantum key distribution and Einstein–Podolsky–Rosen steering via dispersive optics Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-12-01 Kai-Chi Chang, Murat Can Sarihan, Xiang Cheng, Zheshen Zhang, Chee Wei Wong
Quantum key distribution (QKD) has established itself as a groundbreaking technology, showcasing inherent security features that are fundamentally proven. Qubit-based QKD protocols that rely on binary encoding encounter an inherent constraint related to the secret key capacity. This limitation restricts the maximum secret key capacity to one bit per photon. On the other hand, qudit-based QKD protocols
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Clock synchronization with pulsed single photon sources Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-12-01 Christopher Spiess, Fabian Steinlechner
Photonic quantum technology requires precise, time-resolved identification of photodetection events. In distributed quantum networks with spatially separated and drifting time references, achieving high precision is particularly challenging. Here we build on recent advances of using single-photons for time transfer and employ and quantify a fast postprocessing scheme designed to pulsed single-photon
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Variational quantum state discriminator for supervised machine learning Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-11-21 Dongkeun Lee, Kyunghyun Baek, Joonsuk Huh, Daniel K Park
Quantum state discrimination (QSD) is a fundamental task in quantum information processing with numerous applications. We present a variational quantum algorithm that performs the minimum-error QSD, called the variational quantum state discriminator (VQSD). The VQSD uses a parameterized quantum circuit that is trained by minimizing a cost function derived from the QSD, and finds the optimal positive-operator
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Quantum logical controlled-NOT gate in a lithium niobate-on-insulator photonic quantum walk Quantum Sci. Technol. (IF 6.7) Pub Date : 2023-11-17 Robert J Chapman, Samuel Häusler, Giovanni Finco, Fabian Kaufmann, Rachel Grange
The two-qubit controlled-NOT gate is one of the central entangling operations in quantum information technology. The controlled-NOT gate for single photon qubits is normally realized as a network of five individual beamsplitters on six optical modes. Quantum walks (QWs) are an alternative photonic architecture involving arrays of coupled waveguides, which have been successful for investigating condensed