Coherent Control Research Articles

Robust Quantum Gate Optimization with First-Order Derivatives of Ion-Phonon and Ion-Ion Coupling in Trapped Ions

Abstract Trapped ion hardware has made significant progress recently and is now one of the leading platforms for quantum computing. To construct two-qubit gates in trapped ions, experimental manipulation approaches for ion chains are becoming increasingly prevalent. Given the restricted control technology, how implementing high-fidelity quantum gate operations is crucial. Many works in current pulse design optimization focus on ion-phonon and effective ion-ion coupling while ignoring the first-order derivatives terms expansion impacts of these two terms brought on by experiment defects. This paper proposes a novel robust quantum control optimization method in trapped ions. By introducing the first-order derivatives terms caused by the error into the optimization cost function, we generate an extremely robust Mølmer-Sørensen gate with infidelity below 10-3 under drift noise range ±10 kHz, the relative robustness achieves a tolerance of ±5%, compared to the 200 kHz frequency spacing between phonon modes, and for time noise drift, the tolerance reached to 2%. Our work reveals the vital role of the first-order derivatives terms of coupling in trapped ion pulse control optimization, especially the first-order derivatives terms of ion-ion coupling. It provides a robust optimization scheme for realizing more efficient entangled states in trapped ion platforms.

Deterministic multi-phonon entanglement between two mechanical resonators on separate substrates

Mechanical systems have emerged as a compelling platform for applications in quantum information, leveraging advances in the control of phonons, the quanta of mechanical vibrations. Experiments have demonstrated the control and measurement of phonon states in mechanical resonators, and while dual-resonator entanglement has been demonstrated, more complex entangled states remain a challenge. Here, we demonstrate rapid multi-phonon entanglement generation and subsequent tomographic analysis, using a scalable platform comprising two surface acoustic wave resonators on separate substrates, each connected to a superconducting qubit. We synthesize a mechanical Bell state with a fidelity of F=0.872±0.002, and a multi-phonon entangled N = 2 N00N state with a fidelity of F=0.748±0.008. The compact, modular, and scalable platform we demonstrate will enable further advances in the quantum control of complex mechanical systems.

Quantum control of ion-atom collisions beyond the ultracold regime.

Tunable scattering resonances are crucial for controlling atomic and molecular systems. However, their use has so far been limited to ultracold temperatures. These conditions remain hard to achieve for most hybrid trapped ion-atom systems-a prospective platform for quantum technologies and fundamental research. Here, we measure inelastic collision probabilities for Sr+ + Rb and use them to calibrate a comprehensive theoretical model of ion-atom collisions. Our theoretical results, compared with experimental observations, confirm that quantum interference effects persist to the multiple-partial-wave regime, leading to the pronounced state and mass dependence of the collision rates. Using our model, we go beyond interference and identify a rich spectrum of Feshbach resonances at moderate magnetic fields with the Rb atom in its lower (f = 1) hyperfine state, which persist at temperatures as high as 1 millikelvin. Future observation of these predicted resonances should allow precise control of the short-range dynamics in Sr+ + Rb collisions under unprecedentedly warm conditions.

Electronic Noise Considerations for Designing Integrated Solid‐State Quantum Memories

AbstractAs quantum networks expand and are deployed outside research laboratories, a need arises to design and integrate compact control electronics for each memory node. It is essential to understand the performance requirements for such systems, especially concerning tolerable levels of noise, since these specifications dramatically affect a system's design complexity and cost. Here, using an approach that can be easily generalized across quantum‐hardware platforms, a case study based on nitrogen‐vacancy (NV) centers in diamond is presented. The effects of phase noise and timing jitter in the control system in conjunction are modeled and experimentally verified with the spin qubit's environmental noise. The impact of different phase noise characteristics on the fidelity of dynamical decoupling sequences is also considered. The results demonstrate a procedure to specify design requirements for integrated quantum control signal generators for solid‐state spin qubits, depending on their coherence time, intrinsic noise spectrum, and required fidelity.

Automated graph-based detection of quantum control schemes: Application to molecular laser cooling

Automated graph-based detection of quantum control schemes: Application to molecular laser cooling

Identification of an upper limit to the laser pulse duration in photonic band-edge liquid crystal lasers

Photonic band-edge liquid crystal (LC) lasers are an exciting field of research, offering potential in a range of applications from medical imaging to holographic projection. Much work has been done on improving the performance of LC lasers. However, due to historical limitations in pumping techniques, very little experimental work into the temporal dynamics of LC lasers has been published. In this paper, a laser diode pump source with a variable pulse duration is used to investigate the temporal characteristics of the resultant LC laser pulses, while maintaining a constant ratio of pump pulse energy to LC laser threshold. The existence of an upper limit to the output pulse duration of stimulated emission from an LC laser is presented, with a value of 3.5 (±0.1) ns for a DCM-doped cell and 5.2 (±0.2) ns for a Coumarin504-doped cell, irrespective of the laser diode pump pulse lengths, which exceed these values. Evidence is provided to show that the remainder of the optical energy within the pump pulse results in fluorescence emission. The results are in good agreement with the theory of organic dye dynamics and may provide possible future opportunities for electronic control of laser linewidth and coherence in addition to pump parameter optimization for improved LC laser performance.

Mechanism of Hydrogen Generation Catalyzed by a Single Atom and Its Spin Regulation.

Single-atom catalysts exhibit the excellent catalytic activity and selectivity, making them widely applicable in the fields of advanced materials, environmental science, and chemical synthesis. However, understanding the mechanism of single-atom catalytic reactions, such as the hydrogen generation reaction, is still challenging, which notably hampers the optimization and precise control of the reaction. Here, we immobilize a single-metal atom model catalyst into a single-molecule electrical detection platform for in situ monitoring of the catalytic hydrogen generation process at the single-event level. In combination with theoretical and experimental studies, the catalytic mechanisms of the hydrogen generation reaction, especially the selection of the catalytic center through charge, spin, and orbital quantum control, are elucidated. In addition, a hydrogen generation process via quantum spin-induced catalysis is observed, in which the turnover frequency increases by about 65 times at a magnetic field of 50 mT. This study provides valuable insights into the intrinsic mechanism of single-metal atom catalysis and opens up unique avenues for their precise control, thus offering a useful strategy for efficiently developing clean energy.

The detection of seawater elements by virtual polarizer capable of coherent perfect ultra-wideband polarization control

The detection of seawater elements by virtual polarizer capable of coherent perfect ultra-wideband polarization control

Robust quantum control in closed and open systems: Theory and practice

Robust control of quantum systems is an increasingly relevant field of study amidst the second quantum revolution, but there remains a gap between taming quantum physics and robust control in its modern analytical form that culminated in fundamental performance bounds. With certain exceptions such as quantum optical systems that can be modeled as linear stochastic differential equations, quantum systems are not amenable to linear, time-invariant, measurement-based robust control techniques, and thus novel gap-bridging techniques must be developed. This survey is written for control theorists to provide a review of the current state of quantum control and outline the challenges faced in trying to apply modern robust control to quantum systems. We present issues that arise when applying classical robust control theory to quantum systems, typical methods used by quantum physicists to explore such systems and their robustness, as well as a discussion of open problems to be addressed in the field. We focus on general, practical applications and recent work to enable control researchers to contribute to advancing this burgeoning field.

Unveiling hidden geometric phase of neutron spin rotation in the Bitter–Dubbers experiment

Abstract We propose a novel framework to describe geometric phases in quantum systems under non-adiabatic conditions by introducing the concept of a hidden geometric phase. Conventional geometric phases, such as the Berry phase, rely on adiabatic evolution, limiting their applicability in rapidly changing systems. Here, we remove this constraint by reinterpreting the geometric phase as arising from a dynamically evolving reference basis, independent of the external topological features. The hidden phase is revealed through transitionless quantum control techniques, ensuring pure geometric phase accumulation even in non-adiabatic regimes. Our method offers an exact solution to the neutron spin rotation phase in the Bitter–Dubbers experiment, aligning more closely with experimental data without depending on adiabatic approximations. This unexpected result broadens our understanding of the geometric phase observed in neutron spin rotation beyond the adiabatic conditions that are conventionally required.

Approximating exponentials of commutators by optimized product formulas

Trotter product formulas constitute a cornerstone quantum Hamiltonian simulation technique. However, the efficient implementation of Hamiltonian evolution of nested commutators remains an under explored area. In this work, we construct optimized product formulas of orders 3–6 approximating the exponential of a commutator of two arbitrary operators in terms of the exponentials of the operators involved. The new schemes require a reduced number of exponentials and thus provide more efficient approximations than other previously published alternatives. They can also be used as basic methods in recursive procedures to increase the order of approximation. We expect this research will improve the efficiency of quantum control protocols, as well as quantum algorithms such as the Zassenhaus-based product formula, Magnus operator-based time-dependent simulation, and product formula schemes with modified potentials.

Superconducting quantum computing optimization based on multi-objective deep reinforcement learning

Deep reinforcement learning is considered an effective technology in quantum optimization and can provide strategies for optimal control of complex quantum systems. More precise measurements require simulation control at multiple experimental stages. Based on this, we improved a multi-objective deep reinforcement learning method in mathematical convex optimization theory for multi-process quantum optimal control optimization. By setting the single-process quantum control optimization result as a multi-objective optimization truncation threshold and reward function transfer strategy, we finally gave a global optimal solution that considers multiple influencing factors, rather than a local optimal solution that only targets a certain error. This method achieved excellent computational results on superconducting qubits. Optimum control of multi-process quantum computing can be achieved only by regulating the microwave pulse parameters of superconducting qubits, and such a set of global parameter values and control strategies are given.

Alternative illumination system for extreme ultraviolet mask inspection based on Fourier synthesis technology

This study proposes an alternative illuminator based on the Fourier synthesis technology that provides a powerful and flexible way of controlling the coherent properties of illumination for extreme ultraviolet mask inspection. The illuminator achieves coherence control by programming the incident beam scanning a Fresnel zone plate and thus can provide free pupil-fill patterns. In this work, a visible laser-based laboratory microscopic imaging platform has been developed using the illuminator. The spatial resolution and the dense-line image contrast were experimentally evaluated for various coherence factors when a disk and a dipole pupil-fill pattern were applied, respectively. The results are in good agreement with the theoretical calculation of the Rayleigh criterion and the contrast transfer function, which validates the proposed new illuminator. The reliable laser-based imaging platform sheds light on designing and improving EUV mask inspection systems based on synchrotron radiation light sources. The proposed new alternative illuminator will be used in an EUV microscopy at the Shanghai Synchrotron Radiation Facility in future work.

Cryogenic in-memory computing using magnetic topological insulators.

Machine learning algorithms have proven to be effective for essential quantum computation tasks such as quantum error correction and quantum control. Efficient hardware implementation of these algorithms at cryogenic temperatures is essential. Here we utilize magnetic topological insulators as memristors (termed magnetic topological memristors) and introduce a cryogenic in-memory computing scheme based on the coexistence of a chiral edge state and a topological surface state. The memristive switching and reading of the giant anomalous Hall effect exhibit high energy efficiency, high stability and low stochasticity. We achieve high accuracy in a proof-of-concept classification task using four magnetic topological memristors. Furthermore, our algorithm-level and circuit-level simulations of large-scale neural networks demonstrate software-level accuracy and lower energy consumption for image recognition and quantum state preparation compared with existing magnetic memristor and complementary metal-oxide-semiconductor technologies. Our results not only showcase a new application of chiral edge states but also may inspire further topological quantum-physics-based novel computing schemes.

Quantum Coherent and Measurement Feedback Control Based on Atoms Coupled with a Semi-infinite Waveguide

Quantum Coherent and Measurement Feedback Control Based on Atoms Coupled with a Semi-infinite Waveguide

Coherent competition and control between three-wave mixing and four-wave mixing in superconducting circuits

Coherent competition and control between three-wave mixing and four-wave mixing in superconducting circuits

Exploring the job demands and resources and work-related sense of coherence of preschool educators working with children in need of special support

Inclusion of children needing special support presents challenges for preschool educators. Understanding factors that enhance their well-being can improve their ability to meet all children’s needs. This cross-sectional study investigated 90 preschool educators perceived job demands and resources related to working with children in need of special support, and work-related sense of coherence (comprehensibility, manageability, meaningfulness). Analyses of group differences between preschool teachers and child carers revealed no significant differences in the experience of job demands and resources but preschool teachers reported a higher degree of meaningfulness at work compared to child carers. Correlation analyses showed that job resources were all intercorrelated and either inversely correlated or uncorrelated with job demands. Job demands were also inversely correlated to sense of coherence. Linear regression results indicated that a higher work-related sense of coherence and self-perceived control predicted lower self-perceived job demands, even after controlling for social support, growth/development, child group size and insufficient reflection time. This study underscores the need to integrate a sense of comprehensibility, manageability, and meaningfulness at work to improve well-being and to cope with the emotional, cognitive, and organisational demands of working with children needing special support.

Violence, change and continuity in times of transition

Abstract This article discusses how analyses of conflict often overlook competing interpretations of violence in times of change and transition. As a result, in historiography as well as in public discourse, wars just ‘end’ while neglecting the phenomena that are overlapping war and peaceful periods. This article argues that, along the dimensions of state domination, economy and law, alternative periodizations are required to do justice to actors whose politics are often not very strategic yet important for the political dynamics of transitions. Violence, we argue, can be used as a marker and entry point into the complex politics of change, which are motivated by ideology, opportunity, societal dynamics and lack of coherent control by the state or other institutions.

Coherent Photocurrent Injection through Quantum Interference between Stimulated Electronic Raman Scattering and Single-Photon Absorption in Intrinsic Graphene.

The physical picture for photocurrent injection and coherent control in intrinsic graphene under two-color laser excitation remains obscure. Previously, photocurrent injection of intrinsic graphene was attributed to the quantum interference between two electronic transition pathways of single-photon and two-photon absorptions as well as layer-to-layer coupling. Here, we show that quantum interference between stimulated electronic Raman scattering and single-photon absorption plays a very important role in contributing to the total photocurrent, while interlayer coupling does not sufficiently affect the photocurrent injection, which is in contrast to the previous interpretation of the experimental results on photocurrent injection and coherent control. Our findings may change the basic understanding of the physical picture of electron transitions and photocurrent injection, which may benefit the design and fabrication of graphene-based optoelectronic devices.

Decoherence-free many-body Hamiltonians in nonlinear waveguide quantum electrodynamics

Enhancing interactions in many-body quantum systems, while protecting them from environmental decoherence, is at the heart of many quantum technologies. Waveguide quantum electrodynamics is a promising platform for achieving this, as it hosts infinite-range interactions and decoherence-free subspaces of quantum emitters. However, as coherent interactions between emitters are typically washed out in the wavelength-spacing regime hosting decoherence-free states, coherent control over the latter becomes limited, and many-body Hamiltonians in this important regime remain out of reach. Here we show that by incorporating emitter arrays with nonlinear waveguides hosting parametric gain, we obtain a unique class of many-body interaction Hamiltonians with coupling strengths that increase with emitter spacing, and persist even for wavelength-spaced arrays. We then propose to use these Hamiltonians to coherently generate decoherence-free states directly from the ground state, using only global squeezing drives, without the need for local addressing of individual emitters. Interestingly, we find that the dynamics approaches a unitary evolution in the limit of weak intrawaveguide squeezing, and we discuss potential experimental realizations of this effect. Our results pave the way towards coherent control protocols in waveguide quantum electrodynamics, with applications including quantum computing, simulation, memory, and nonclassical light generation. Published by the American Physical Society 2025