-
Thermodynamic sensing of quantum nonlinear noise correlations Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-22 Nilakantha Meher, Tomáš Opatrný, Gershon Kurizki
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
-
Photonic variational quantum eigensolver using entanglement measurements Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-21 Jinil Lee, Wooyeong Song, Donghwa Lee, Yosep Kim, Seung-Woo Lee, Hyang-Tag Lim, Hojoong Jung, Sang-Wook Han, Yong-Su Kim
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
-
Entanglement-preserving measurement of the Bell parameter on a single entangled pair Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-20 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
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
-
A differentiable quantum phase estimation algorithm Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-13 Davide Castaldo, Soran Jahangiri, Agostino Migliore, Juan Miguel Arrazola, Stefano Corni
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
-
A square-root speedup for finding the smallest eigenvalue Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-12 Alex Kerzner, Vlad Gheorghiu, Michele Mosca, Thomas Guilbaud, Federico Carminati, Fabio Fracas, Luca Dellantonio
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. O~(N/ε) 9 9In this work O~ ignores terms that are polylogarithmic in N or 1/ε . black-box queries to an oracle encoding
-
Ratchet loading and multi-ensemble operation in an optical lattice clock Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-08 Youssef S Hassan, Takumi Kobayashi, Tobias Bothwell, Jacob L Seigel, Benjamin D Hunt, Kyle Beloy, Kurt Gibble, Tanner Grogan, Andrew D Ludlow
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
-
Bang-bang optimal control in coherent spin dynamics of radical pairs in quantum biology Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-08 Ugur G Abdulla, Jose Rodrigues, Pablo Jimenez, Chenming Zhen, Carlos Martino
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
-
Optimal and robust quantum state tomography of star-topology register Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-08 Ran Liu, Yanjun Hou, Ze Wu, Hui Zhou, Jiahui Chen, Zhaokai Li, Xinhua Peng
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
-
Distributing circuits over heterogeneous, modular quantum computing network architectures Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-06 Pablo Andres-Martinez, Tim Forrer, Daniel Mills, Jun-Yi Wu, Luciana Henaut, Kentaro Yamamoto, Mio Murao, Ross Duncan
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
-
Experimental realization of active nonlinear feedback control from hot rubidium vapor Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-02 Xiaozhou Pan, Tianxiang Wei, Kai Zhang, Jietai Jing
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
-
Emergence of noise-induced barren plateaus in arbitrary layered noise models Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-02 M Schumann, F K Wilhelm, A Ciani
In variational quantum algorithms the parameters of a parameterized quantum circuit are optimized in order to minimize a cost function that encodes the solution of the problem. The barren plateau phenomenon manifests as an exponentially vanishing dependence of the cost function with respect to the variational parameters, and thus hampers the optimization process. We discuss how, and in which sense
-
Conditional quantum thermometry—enhancing precision by measuring less Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-02 Akira Sone, Diogo O Soares-Pinto, Sebastian Deffner
Taking accurate measurements of the temperature of quantum systems is a challenging task. The mathematical peculiarities of quantum information make it virtually impossible to measure with infinite precision. In the present paper, we introduce a generalize thermal state, which is conditioned on the pointer states of the available measurement apparatus. We show that this conditional thermal state outperforms
-
Nonequilibrium fluctuations of a quantum heat engine Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-01 Tobias Denzler, Jonas F G Santos, Eric Lutz, Roberto M Serra
The thermodynamic properties of quantum heat engines are stochastic owing to the presence of thermal and quantum fluctuations. We here experimentally investigate the efficiency and nonequilibrium entropy production statistics of a spin-1/2 quantum Otto cycle in a nuclear magnetic resonance setup. We first study the correlations between work and heat within a cycle by extracting their joint distribution
-
Integer programming using a single atom Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-01 Kapil Goswami, Peter Schmelcher, Rick Mukherjee
Integer programming (IP), as the name suggests is an integer-variable-based approach commonly used to formulate real-world optimization problems with constraints. Currently, quantum algorithms reformulate the IP into an unconstrained form through the use of binary variables, which is an indirect and resource-consuming way of solving it. We develop an algorithm that maps and solves an IP problem in
-
Counterfactuality, back-action, and information gain in multi-path interferometers Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-24 Jonte R Hance, Tomonori Matsushita, Holger F Hofmann
The presence of an absorber in one of the paths of an interferometer changes the output statistics of that interferometer in a fundamental manner. Since the individual quantum particles detected at any of the outputs of the interferometer have not been absorbed, any non-trivial effect of the absorber on the distribution of these particles over these paths is a counterfactual effect. Here, we quantify
-
Beyond quantum annealing: optimal control solutions to maxcut problems Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-18 Giovanni Pecci, Ruiyi Wang, Pietro Torta, Glen Bigan Mbeng, Giuseppe Santoro
Quantum Annealing (QA) relies on mixing two Hamiltonian terms, a simple driver and a complex problem Hamiltonian, in a linear combination. The time-dependent schedule for this mixing is often taken to be linear in time: improving on this linear choice is known to be essential and has proven to be difficult. Here, we present different techniques for improving on the linear-schedule QA along two directions
-
Asymptotic teleportation scheme bridging between standard and port-based teleportation Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-18 Ha Eum Kim, Kabgyun Jeong
Various modified quantum teleportation schemes are proposed to overcome experimental constraints or to meet specific application requirements for quantum communication. Hence, most schemes are developed and studied with unique methodologies, each with its own inherent challenges. Our research focuses on interconnecting these schemes, which appear to be unrelated to each other, based on the idea that
-
Lift-connected surface codes Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-17 Josias Old, Manuel Rispler, Markus Müller
We use the recently introduced lifted product to construct a family of quantum low density parity check codes (QLDPC codes). The codes we obtain can be viewed as stacks of surface codes that are interconnected, leading to the name lift-connected surface (LCS) codes. LCS codes offer a wide range of parameters—a particularly striking feature is that they show interesting properties that are favorable
-
Towards interpretable quantum machine learning via single-photon quantum walks Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-15 Fulvio Flamini, Marius Krumm, Lukas J Fiderer, Thomas Müller, Hans J Briegel
Variational quantum algorithms represent a promising approach to quantum machine learning where classical neural networks are replaced by parametrized quantum circuits. However, both approaches suffer from a clear limitation, that is a lack of interpretability. Here, we present a variational method to quantize projective simulation (PS), a reinforcement learning model aimed at interpretable artificial
-
A chip-integrated homodyne detection system with enhanced bandwidth performance for quantum applications Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-15 Si Qi Ng, Gong Zhang, Charles Lim, Chao Wang
The rapid development of quantum technology has driven the need for high-performance quantum signal processing modules. Balanced homodyne detector (BHD) is one of the most promising options for practical quantum state measurement, providing substantial advantages of cost-effectiveness, no cooling requirement, and system compactness. However, due to the stringent requirements in BHD design, it typically
-
Quanto: optimizing quantum circuits with automatic generation of circuit identities Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-12 Jessica Pointing, Oded Padon, Zhihao Jia, Henry Ma, Auguste Hirth, Jens Palsberg, Alex Aiken
Existing quantum compilers focus on mapping a logical quantum circuit to a quantum device and its native quantum gates. Only simple circuit identities are used to optimize the quantum circuit during the compilation process. This approach misses more complex circuit identities, which could be used to optimize the quantum circuit further. We propose Quanto, the first quantum optimizer that automatically
-
Interplay among entanglement, measurement incompatibility, and nonlocality Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-10 Yuwei Zhu, Xingjian Zhang, Xiongfeng Ma
Nonlocality, manifested by the violation of Bell inequalities, indicates entanglement within a joint quantum system. A natural question is how much entanglement is required for a given nonlocal behavior. Here, we explore this question by quantifying entanglement using a family of generalized Clauser–Horne–Shimony–Holt-type Bell inequalities. Given a Bell-inequality violation, we derive analytical lower
-
Non-unitary Trotter circuits for imaginary time evolution Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-09 Chiara Leadbeater, Nathan Fitzpatrick, David Muñoz Ramo, Alex J W Thom
We propose an imaginary time equivalent of the well-established Pauli gadget primitive for Trotter-decomposed real time evolution, using mid-circuit measurements on a single ancilla qubit. Imaginary time evolution (ITE) is widely used for obtaining the ground state (GS) of a system on classical hardware, computing thermal averages, and as a component of quantum algorithms that perform non-unitary evolution
-
Bases for optimising stabiliser decompositions of quantum states Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-08 Nadish de Silva, Ming Yin, Sergii Strelchuk
Stabiliser states play a central role in the theory of quantum computation. For example, they are used to encode computational basis states in the most common quantum error correction schemes. Arbitrary quantum states admit many stabiliser decompositions: ways of being expressed as a superposition of stabiliser states. Understanding the structure of stabiliser decompositions has significant applications
-
Collective biphoton temporal waveform of photon-pair generated from Doppler-broadened atomic ensemble Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-08 Heewoo Kim, Hansol Jeong, Han Seb Moon
Photonic quantum states generated from atomic ensembles will play important roles in future quantum networks and long-distance quantum communication because their advantages, such as universal identity and narrow spectral bandwidth, are essential for quantum nodes and quantum repeaters based on atomic ensembles. In this study, we report the collectively coherent superposition of biphoton wavefunction
-
Quantum computer-enabled receivers for optical communication Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-08 John Crossman, Spencer Dimitroff, Lukasz Cincio, Mohan Sarovar
Optical communication is the standard for high-bandwidth information transfer in today’s digital age. The increasing demand for bandwidth has led to the maturation of coherent transceivers that use phase- and amplitude-modulated optical signals to encode more bits of information per transmitted pulse. Such encoding schemes achieve higher information density, but also require more complicated receivers
-
Multi-qubit dynamical decoupling for enhanced crosstalk suppression Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-04 Siyuan Niu, Aida Todri-Sanial, Nicholas T Bronn
Dynamical decoupling (DD) is one of the simplest error suppression methods, aiming to enhance the coherence of qubits in open quantum systems. Moreover, DD has demonstrated effectiveness in reducing coherent crosstalk, one major error source in near-term quantum hardware, which manifests from two types of interactions. Static crosstalk exists in various hardware platforms, including superconductor
-
Efficient and practical quantum compiler towards multi-qubit systems with deep reinforcement learning ∗ ∗ The authors list is in alphabetical order. Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-03 Qiuhao Chen, Yuxuan Du, Yuliang Jiao, Xiliang Lu, Xingyao Wu, Qi Zhao
Efficient quantum compiling is essential for complex quantum algorithms realization. The Solovay–Kitaev (S–K) theorem offers a theoretical lower bound on the required operations for approaching any unitary operator. However, it is still an open question that this lower bound can be actually reached in practice. Here, we present an efficient quantum compiler which, for the first time, approaches the
-
Reducing hardware requirements for entanglement distribution via joint hardware-protocol optimization Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-02 Adrià Labay Mora, Francisco Ferreira da Silva, Stephanie Wehner
We conduct a numerical investigation of fiber-based entanglement distribution over distances of up to 1600 km using a chain of processing-node quantum repeaters. We determine minimal hardware requirements while simultaneously optimizing over protocols for entanglement generation and entanglement purification, as well as over strategies for entanglement swapping. Notably, we discover that through an
-
Constructive plaquette compilation for the parity architecture Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-07-01 Roeland ter Hoeven, Benjamin E Niehoff, Sagar Sudhir Kale, Wolfgang Lechner
Parity compilation is the challenge of laying out the required constraints for the parity mapping in a local way. We present the first constructive compilation algorithm for the parity architecture using plaquettes for arbitrary higher-order optimization problems. This enables adiabatic protocols, where the plaquette layout can natively be implemented, as well as fully parallelized digital circuits
-
Ab-initio tree-tensor-network digital twin for quantum computer benchmarking in 2D Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-28 Daniel Jaschke, Alice Pagano, Sebastian Weber, Simone Montangero
Large-scale numerical simulations of the Hamiltonian dynamics of a noisy intermediate scale quantum computer—a digital twin—could play a major role in developing efficient and scalable strategies for tuning quantum algorithms for specific hardware. Via a two-dimensional tensor network digital twin of a Rydberg atom quantum computer, we demonstrate the feasibility of such a program. In particular, we
-
Two-dimensional coherent spectrum of high-spin models via a quantum computing approach Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-26 Martin Mootz, Peter P Orth, Chuankun Huang, Liang Luo, Jigang Wang, Yong-Xin Yao
We present and benchmark a quantum computing approach to calculate the two-dimensional coherent spectrum (2DCS) of high-spin models. Our approach is based on simulating their real-time dynamics in the presence of several magnetic field pulses, which are spaced in time. We utilize the adaptive variational quantum dynamics simulation algorithm for the study due to its compact circuits, which enables
-
Towards a realistic model for cavity-enhanced atomic frequency comb quantum memories Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-25 Shahrzad Taherizadegan, Jacob H Davidson, Sourabh Kumar, Daniel Oblak, Christoph Simon
Atomic frequency comb (AFC) quantum memory is a favorable protocol in long distance quantum communication. Putting the AFC inside an asymmetric optical cavity enhances the storage efficiency but makes the measurement of the comb properties challenging. We develop a theoretical model for cavity-enhanced AFC quantum memory that includes the effects of dispersion, and show a close alignment of the model
-
Multi-variable integration with a variational quantum circuit Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-25 Juan M Cruz-Martinez, Matteo Robbiati, Stefano Carrazza
In this work we present a novel strategy to evaluate multi-variable integrals with quantum circuits. The procedure first encodes the integration variables into a parametric circuit. The obtained circuit is then derived with respect to the integration variables using the parameter shift rule technique. The observable representing the derivative is then used as the predictor of the target integrand function
-
Spin resonance spectroscopy with an electron microscope Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-24 Philipp Haslinger, Stefan Nimmrichter, Dennis Rätzel
Coherent spin resonance methods, such as nuclear magnetic resonance and electron spin resonance spectroscopy, have led to spectrally highly sensitive, non-invasive quantum imaging techniques. Here, we propose a pump-probe spin resonance spectroscopy approach, designed for electron microscopy, based on microwave pump fields and electron probes. We investigate how quantum spin systems couple to electron
-
Local coherence by thermalized intra-system coupling Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-24 Michal Kolář, Radim Filip
Quantum superposition of energy eigenstates can appear autonomously in a single quantum two-level system coupled to a low-temperature thermal bath, if such coupling has a proper composite nature. We propose here a principally different and more feasible approach employing engineered interactions between two-level systems being thermalized into a global Gibbs state by weakly coupled thermal bath at
-
A modular optically pumped magnetometer system Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-19 T Coussens, A Gialopsou, C Abel, M G Bason, T M James, W Evans, M T M Woodley, D Nightingale, D Nicolau, L Page, F Oručević, P Krüger
To address the demands in healthcare and industrial settings for spatially resolved magnetic imaging, we present a modular optically pumped magnetometer (OPM) system comprising a multi-sensor array of highly sensitive quantum magnetometers. This system is designed and built to facilitate fast prototyping and testing of new measurement schemes by enabling quick reconfiguration of the self-contained
-
Quantum Fisher kernel for mitigating the vanishing similarity issue Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-17 Yudai Suzuki, Hideaki Kawaguchi, Naoki Yamamoto
Quantum kernel (QK) methods exploit quantum computers to calculate QKs for the use of kernel-based learning models. Despite a potential quantum advantage of the method, the commonly used fidelity-based QK suffers from a detrimental issue, which we call the vanishing similarity issue; the exponential decay of the expectation value and the variance of the QK deteriorates implementation feasibility and
-
Mode analysis of spin field of thermal atomic ensembles Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-13 Weiyi Wang, Mingming Xia, Wei Quan, Kai Wei
The spin dynamics in a thermal atomic vapor cell have been investigated thoroughly over the past decades and have proven to be successful in quantum metrology and memory owing to their long coherent time and manipulation convenience. The existing mean field analysis of spin dynamics among the whole cell is sometimes inaccurate due to the non-uniformity of the ensemble and spatial coupling of multi-physical
-
Analog quantum simulation of partial differential equations Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-11 Shi Jin, Nana Liu
Quantum simulators were originally proposed for simulating one partial differential equation (PDE) in particular—Schrödinger’s equation. Can quantum simulators also efficiently simulate other PDEs? While most computational methods for PDEs—both classical and quantum—are digital (they must be discretised first), PDEs have continuous degrees of freedom. This suggests that an analog representation can
-
Quantum kernels for classifying dynamical singularities in a multiqubit system Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-11 Diego Tancara, José Fredes, Ariel Norambuena
Dynamical quantum phase transition is a critical phenomenon involving out-of-equilibrium states and broken symmetries without classical analogy. However, when finite-sized systems are analyzed, dynamical singularities of the rate function can appear, leading to a challenging physical characterization when parameters are changed. Here, we report a quantum support vector machine algorithm that uses quantum
-
Hacking coherent-one-way quantum key distribution with present-day technology Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-06-06 Javier Rey-Domínguez, Álvaro Navarrete, Peter van Loock, Marcos Curty
Recent results have shown that the secret-key rate of coherent-one-way (COW) quantum key distribution (QKD) scales quadratically with the system’s transmittance, thus rendering this protocol unsuitable for long-distance transmission. This was proven by using a so-called zero-error attack, which relies on an unambiguous state discrimination (USD) measurement. This type of attack allows the eavesdropper
-
System-bath correlations and finite-time operation enhance the efficiency of a dissipative quantum battery Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-30 Daniel Feliú, Felipe Barra
The reduced state of a small system strongly coupled to a thermal bath may be athermal and used as a small battery once disconnected. The unitarily extractable energy (a.k.a. ergotropy) will be negligible if the disconnecting process is too slow. To study the efficiency of this battery, we consider the cycle of disconnecting, extracting, and connecting the battery back to the bath. Efficiency, i.e
-
Optimal quantum metrology of two-photon absorption Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-29 Athena Karsa, Ranjith Nair, Andy Chia, Kwang-Geol Lee, Changhyoup Lee
Two-photon absorption (TPA) is a nonlinear optical process with wide-ranging applications from spectroscopy to super-resolution imaging. Despite this, the precise measurement and characterisation of TPA parameters are challenging due to their inherently weak nature. We study the potential of single-mode quantum light to enhance TPA parameter estimation through the quantum Fisher information (QFI).
-
On the optimality of the radical-pair quantum compass Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-28 Luke D Smith, Jonas Glatthard, Farhan T Chowdhury, Daniel R Kattnig
Quantum sensing enables the ultimate precision attainable in parameter estimation. Circumstantial evidence suggests that certain organisms, most notably migratory songbirds, also harness quantum-enhanced magnetic field sensing via a radical-pair-based chemical compass for the precise detection of the weak geomagnetic field. However, what underpins the acuity of such a compass operating in a noisy biological
-
On-chip tunable quantum interference in a lithium niobate-on-insulator photonic integrated circuit Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-28 Andreas Maeder, Giovanni Finco, Fabian Kaufmann, Alessandra Sabatti, Jost Kellner, Robert J Chapman, Rachel Grange
Programmable interferometric circuits are at the heart of integrated quantum photonic processors. While the lithium niobate-on-insulator platform has the potential to advance integrated quantum photonics due to its strong nonlinearity and tight mode confinement, the demonstration of reconfigurable two-photon interference has not yet been achieved. Here, we design, fabricate and characterize the building
-
Controlling the interactions in a cold atom quantum impurity system Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-28 Thomas Hewitt, Tom Bertheas, Manan Jain, Yusuke Nishida, Giovanni Barontini
We implement an experimental architecture in which a single atom of K is trapped in an optical tweezer, and is immersed in a bath of Rb atoms at ultralow temperatures. In this regime, the motion of the single trapped atom is confined to the lowest quantum vibrational levels. This realizes an elementary and fully controllable quantum impurity system. For the trapping of the K atom, we use a species-selective
-
Vanadium in silicon carbide: telecom-ready spin centres with long relaxation lifetimes and hyperfine-resolved optical transitions Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-22 Thomas Astner, Philipp Koller, Carmem M Gilardoni, Joop Hendriks, Nguyen Tien Son, Ivan G Ivanov, Jawad Ul Hassan, Caspar H van der Wal, Michael Trupke
Vanadium in silicon carbide (SiC) is emerging as an important candidate system for quantum technology due to its optical transitions in the telecom wavelength range. However, several key characteristics of this defect family including their spin relaxation lifetime (T1), charge state dynamics, and level structure are not fully understood. In this work, we determine the T1 of an ensemble of vanadium
-
Unifying quantum verification and error-detection: theory and tools for optimisations Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-21 Theodoros Kapourniotis, Elham Kashefi, Dominik Leichtle, Luka Music, Harold Ollivier
With the advent of cloud-based quantum computing, it has become vital to provide strong guarantees that computations delegated by clients to quantum service providers have been executed faithfully. Secure—blind and verifiable—delegated quantum computing (SDQC) has emerged as one of the key approaches to address this challenge, yet current protocols lack at least one of the following three ingredients:
-
Single-step parity check gate set for quantum error correction Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-21 Gözde Üstün, Andrea Morello, Simon Devitt
A key requirement for an effective quantum error correction (QEC) scheme is that the physical qubits have error rates below a certain threshold. The value of this threshold depends on the details of the specific QEC scheme, and its hardware-level implementation. This is especially important with parity-check circuits, which are the fundamental building blocks of QEC codes. The standard way of constructing
-
Perspective on new implementations of atomtronic circuits Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-21 Juan Polo, Wayne J Chetcuti, Enrico C Domanti, Philip Kitson, Andreas Osterloh, Francesco Perciavalle, Vijay Pal Singh, Luigi Amico
In this article, we provide perspectives for atomtronics circuits on quantum technology platforms beyond simple bosonic or fermionic cold atom matter-wave currents. Specifically, we consider (i) matter-wave schemes with multi-component quantum fluids; (ii) networks of Rydberg atoms that provide a radically new concept of atomtronics circuits in which the flow, rather than in terms of matter, occurs
-
Benchmarking Bayesian quantum estimation Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-21 Valeria Cimini, Emanuele Polino, Mauro Valeri, Nicolò Spagnolo, Fabio Sciarrino
The quest for precision in parameter estimation is a fundamental task in different scientific areas. The relevance of this problem thus provided the motivation to develop methods for the application of quantum resources to estimation protocols. Within this context, Bayesian estimation offers a complete framework for optimal quantum metrology techniques, such as adaptive protocols. However, the use
-
Sketching phase diagrams using low-depth variational quantum algorithms Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-21 Jan Lukas Bosse, Raul A Santos, Ashley Montanaro
Mapping out phase diagrams of quantum systems using classical simulations can be challenging or intractable due to the computational resources required to simulate even small quantum systems far away from the thermodynamic limit. We investigate using quantum computers and the variational quantum eigensolver (VQE) for this task. In contrast to the task of preparing the exact ground state using VQE,
-
Multiparameter critical quantum metrology with impurity probes Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-16 George Mihailescu, Abolfazl Bayat, Steve Campbell, 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- 12 impurity, which can be manipulated and measured in-situ when embedded in a fermionic environment. Although entanglement between a single impurity probe
-
Analysis of spin-squeezing generation in cavity-coupled atomic ensembles with continuous measurements Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-15 A Caprotti, M Barbiero, M G Tarallo, M G Genoni, 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
-
Resource-efficient quantum principal component analysis Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-14 Youle Wang, 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
-
Sequential optimal selections of single-qubit gates in parameterized quantum circuits Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-05-13 Kaito Wada, Rudy Raymond, Yuki Sato, 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
-
On the relevance of weak measurements in dissipative quantum systems Quantum Sci. Technol. (IF 5.6) 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
-
Privacy-preserving quantum federated learning via gradient hiding Quantum Sci. Technol. (IF 5.6) 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
-
Non-Markovian quantum gate set tomography Quantum Sci. Technol. (IF 5.6) 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