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Authors:H H Jen First page: 023001 Abstract: Photon-mediated dipole–dipole interactions arise from atom-light interactions, which are universal and prevalent in a wide range of open quantum systems. This pairwise and long-range spin-exchange interaction results from multiple light scattering among the atoms. A recent surge of interests and progresses in both experiments and theories promises this core mechanism of collective interactions as a resource to study quantum science and to envision next-generation applications in quantum technology. Here we summarize recent developments in both theories and experiments, where we introduce several central theoretical approaches and focus on cooperative light scattering from small sample of free-space atoms, an atom-waveguide coupled interface that hosts the waveguide QED, and topological quantum optical platforms. The aim of this review is to manifest the essential and distinct features of collective dynamics induced by resonant dipole–dipole interactions and to reveal unprecedented opportunities in enhancing the performance or offering new applications in light manipulations, quantum metrology, quantum computations, and light harvesting innovations. Citation: Quantum Science and Technology PubDate: 2025-03-10T00:00:00Z DOI: 10.1088/2058-9565/adbb86 Issue No:Vol. 10, No. 2 (2025)
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Authors:Jonathan Frazer; Takafumi Ono Jonathan C F Matthews First page: 025033 Abstract: Low loss and high-speed processing of photons is important to photonic quantum information technologies. The speed with which quantum light generation can be modulated impacts the clock rate of photonic quantum computers, the data rate of quantum communication and applications of quantum enhanced radio-frequency sensors. Here we use lossy carrier depletion modulators in a silicon waveguide nonlinear interferometer to modulate photon pair generation probability at 1 gigahertz (GHz) without exposing the generated photons to the phase dependent parasitic loss of the modulators. The super sensitivity of nonlinear interferometers reduces power consumption compared to modulating the driving laser. This can be used for high-speed programmable nonlinearity in waveguide networks for quantum technologies and for optical quantum sensors. Citation: Quantum Science and Technology PubDate: 2025-02-21T00:00:00Z DOI: 10.1088/2058-9565/adb176 Issue No:Vol. 10, No. 2 (2025)
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Authors:Stefano Barison; Javier Robledo Moreno Mario Motta First page: 025034 Abstract: The simulation of molecular electronic structure is an important application of quantum devices. Recently, it has been shown that quantum devices can be effectively combined with classical supercomputing centers in the context of the sample-based quantum diagonalization (SQD) algorithm. This allowed the largest electronic structure quantum simulation to date (77 qubits) and opened near-term devices to practical use cases in chemistry toward the hundred-qubit mark. However, the description of many important physical and chemical properties of those systems, such as photo-absorption/-emission, requires a treatment that goes beyond the ground state alone. In this work, we extend the SQD algorithm to determine low-lying molecular excited states. The extended-SQD method improves over the original SQD method in accuracy, at the cost of an additional computational step. It also improves over quantum subspace expansion based on single and double electronic excitations, a widespread approach to excited states on pre-fault-tolerant quantum devices, in both accuracy and efficiency. We employ the extended SQD method to compute the first singlet (S1) and triplet (T1) excited states of the nitrogen molecule with a correlation-consistent basis set, and the ground- and excited-state properties of the [2Fe-2S] cluster. Citation: Quantum Science and Technology PubDate: 2025-02-27T00:00:00Z DOI: 10.1088/2058-9565/adb781 Issue No:Vol. 10, No. 2 (2025)
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Authors:Chris Gustin; Ryotatsu Yanagimoto, Edwin Ng, Tatsuhiro Onodera Hideo Mabuchi First page: 025035 Abstract: In broadband quantum optical systems, nonlinear interactions among a large number of frequency components induce complex dynamics that may defy heuristic analysis. In this work we introduce a perturbative framework for factoring out reservoir degrees of freedom and establishing a concise effective model (effective field theory) for the remaining system. Our approach combines approximate diagonalization of judiciously partitioned subsystems with master equation techniques. We consider cascaded optical (quadratic) nonlinearities as an example and show that the dynamics can be construed (to leading order) as self-phase modulations of dressed fundamental modes plus cross-phase modulations of dressed fundamental and second-harmonic modes. We then formally eliminate the second-harmonic degrees of freedom and identify emergent features of the fundamental wave dynamics, such as two-photon loss channels, and examine conditions for accuracy of the reduced model in dispersive and dissipative parameter regimes. Our results highlight the utility of system-reservoir methods for deriving accurate, intuitive reduced models for complex dynamics in broadband nonlinear quantum photonics, and may help guide quantum technological proposals in emerging systems where quantum effects become significant at the single-photon level. Citation: Quantum Science and Technology PubDate: 2025-02-28T00:00:00Z DOI: 10.1088/2058-9565/adaedf Issue No:Vol. 10, No. 2 (2025)
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Authors:Mohamed Boubakour; Shimpei Endo, Thomás Fogarty Thomas Busch First page: 025036 Abstract: We propose using the dynamical invariants, also known as the Lewis–Riesenfeld invariants, to speed-up the equilibration of a driven open quantum system. This allows us to reverse engineer the time-dependent master equation that describes the dynamics of the open quantum system and systematically derive a protocol that realizes a shortcut to equilibration. The method does not require additional constraints on the timescale of the dynamics beside the Born–Markov approximation and can be generically applied to boost single particle quantum engines significantly. We demonstrate this with the damped harmonic oscillator, and show that our protocol can achieve high-fidelity control on shorter timescales than simple non-optimized protocols. We find that the system is heated during the dynamics to speed-up the equilibration, which can be considered as an analogue of the Mpemba effect in quantum control. Citation: Quantum Science and Technology PubDate: 2025-03-13T00:00:00Z DOI: 10.1088/2058-9565/adbcce Issue No:Vol. 10, No. 2 (2025)
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Authors:Andrew Patterson; Leigh Lapworth First page: 025037 Abstract: Solving computational fluid dynamics (CFD) problems requires the inversion of a linear system of equations, which can be done using a quantum algorithm for matrix inversion (Gilyén et al 2019 Proc. 51st Annual ACM SIGACT Symp. on Theory of Computing 193–204). However, the number of shots required to measure the output of the system can be prohibitive and remove any advantage obtained by quantum computing. In this work we propose a scheme for measuring the output of a quantum singular value transform (QSVT) matrix inversion algorithm specifically for the CFD use case. We use a quantum signal processing based amplitude estimation algorithm (Rall and Fuller 2023 Quantum7 937) and show how it can be combined with the QSVT matrix inversion algorithm. We perform a detailed resource estimation of the amount of computational resources required for a single iteration of amplitude estimation, and compare the costs of amplitude estimation with the cost of not doing amplitude estimation and measuring the whole wavefunction. We also propose a measurement scheme to reduce the number of amplitudes measured in the CFD example by focussing on large amplitudes only. We simulate the whole CFD loop, finding that thus measuring only a small number of the total amplitudes in the output vector still results in an acceptable level of overall error. Citation: Quantum Science and Technology PubDate: 2025-03-14T00:00:00Z DOI: 10.1088/2058-9565/adbcd0 Issue No:Vol. 10, No. 2 (2025)
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Authors:Philipp Schmidt; Florian Marquardt Naeimeh Mohseni First page: 025038 Abstract: Deep neural networks have demonstrated remarkable efficacy in extracting meaningful representations from complex datasets. This has propelled representation learning as a compelling area of research across diverse fields. One interesting open question is how beneficial representation learning can be for quantum many-body physics, with its notoriously high-dimensional state space. In this work, we showcase the capacity of a neural network that was trained on a subset of physical observables of a many-body system to partially acquire an implicit representation of the wave function. We illustrate this by demonstrating the effectiveness of reusing the representation learned by the neural network to enhance the learning process of another quantity derived from the quantum state. In particular, we focus on how the pre-trained neural network can enhance the learning of entanglement entropy. This is of particular interest as directly measuring the entanglement in a many-body system is very challenging, while a subset of physical observables can be easily measured in experiments. We show the pre-trained neural network learns the dynamics of entropy with fewer resources and higher precision in comparison with direct training on the entanglement entropy. Citation: Quantum Science and Technology PubDate: 2025-03-17T00:00:00Z DOI: 10.1088/2058-9565/adbd6d Issue No:Vol. 10, No. 2 (2025)
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Authors:Ciro Micheletti Diniz; Celso J Villas-Boas Alan C Santos First page: 025039 Abstract: A fast and scalable scheme for multi-qubit resetting in superconducting quantum processors is proposed by exploiting the feasibility of frequency-tunable transmon qubits and transmon-like couplers to engineer a full programmable superconducting erasing head. We demonstrate the emergence of collective effects that lead to a decoherence-free subspace during the erasing process. The presence of such a subspace negatively impacts the device’s performance and has been overlooked in other multi-qubit chips. To circumvent this issue and pave the way to the device’s scalability, we employ tunable frequency couplers to identify a specific set of parameters that enables us to erase even those states within this subspace, ensuring the simultaneous multi-qubit resetting, verified here for the two-qubit case. In contrast, we show that collectivity effects can also emerge as an ingredient to speed up the erasing process. To end, we offer a proposal to build up integrated superconducting processors that can be efficiently connected to erasure heads in a scalable way. Citation: Quantum Science and Technology PubDate: 2025-03-18T00:00:00Z DOI: 10.1088/2058-9565/adbded Issue No:Vol. 10, No. 2 (2025)
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Authors:Mathis Cohen; Laurent Labonté, Romain Dalidet, Sébastien Tanzilli Anthony Martin First page: 025040 Abstract: The interference between two independent photons stands as a crucial aspect of numerous quantum information protocols and technologies. In this work, we leverage fiber-coupled devices, which encompass fibered photon pair-sources and off-the-shelf optics, to demonstrate Hong-Ou-Mandel interference. We employ two distinct single photon sources, namely a heralded single-photon source and a weak coherent laser source, both operating asynchronously in continuous-wave regime. We record two-photon coincidences, showing a state-of-art visibility of 91.9(5)%. This work, compliant with telecom technology, provides realistic backbones for establishing long-range communication based on quantum teleportation in hybrid quantum networks. Citation: Quantum Science and Technology PubDate: 2025-03-18T00:00:00Z DOI: 10.1088/2058-9565/adbb87 Issue No:Vol. 10, No. 2 (2025)
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Authors:Omer Rathore; Alastair Basden, Nicholas Chancellor Halim Kusumaatmaja First page: 025041 Abstract: The application of quantum algorithms to classical problems is generally accompanied by significant bottlenecks when transferring data between quantum and classical states, often negating any intrinsic quantum advantage. Here we address this challenge for a well-known algorithm for linear systems of equations, originally proposed by Harrow, Hassidim and Lloyd (HHL), by adapting it into a predictor–corrector instead of a direct solver. Rather than seeking the solution at the next time step, the goal now becomes determining the change between time steps. This strategy enables the intelligent omission of computationally costly steps commonly found in many classical algorithms, while simultaneously mitigating the notorious readout problems associated with extracting solutions from a quantum state. Random or regularly performed skips instead lead to simulation failure. We demonstrate that our methodology secures a useful polynomial advantage over a conventional application of the HHL algorithm. The practicality and versatility of the approach are illustrated through applications in various fields such as smoothed particle hydrodynamics, plasma simulations, and reactive flow configurations. Moreover, the proposed algorithm is well suited to run asynchronously on future heterogeneous hardware infrastructures and can effectively leverage the synergistic strengths of classical as well as quantum compute resources. Citation: Quantum Science and Technology PubDate: 2025-03-18T00:00:00Z DOI: 10.1088/2058-9565/adbb14 Issue No:Vol. 10, No. 2 (2025)
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