Coherent Control Research Articles (Page 1)

Optically active solid-state spin qubits thrive as an appealing technology for quantum interconnects and quantum networks, thanks to their atomic size, scalable synthesis, long-lived coherence, and ability to coherently interface with flying qubits. Trivalent erbium dopants, in particular, emerge as an attractive candidate due to their emission in the telecom C band and shielded 4f intra-shell spin and optical transitions. Nevertheless, prevailing top-down architectures for rare-earth qubits and devices have not yet achieved simultaneous long optical and spin coherence, which is necessary for efficient long-distance quantum networks. Here, we demonstrate dual Er3+ telecom spin-photon interfaces in two distinct lattice symmetry sites within an epitaxial thin-film platform. By leveraging high matrix crystallinity, controlled proximity of dopants to surfaces, and exploiting host lattice symmetry, we simultaneously achieve kilohertz-level optical linewidth in a strongly symmetry-protected site, and erbium qubit spin coherence times exceeding 10 milliseconds. Additionally, we realize single-shot readout and microwave coherent control of erbium qubits in a fiber-integrated package, enabling rapid deployment and scalability. These advancements highlight the significant potential of high-quality rare-earth qubits and quantum memories assembled using a bottom-up method, paving the way for scalable development of quantum light-matter interfaces tailored for telecommunication quantum networks.

Materials improvement is a powerful approach to reducing loss and decoherence in superconducting qubits, because such improvements can be readily translated to large-scale processors. Recent work improved transmon coherence by using tantalum as a base layer and sapphire as a substrate1. The losses in these devices are dominated by two-level systems with comparable contributions from both the surface and bulk dielectrics2, indicating that both must be tackled to achieve substantial improvements in the state of the art. Here we show that replacing the substrate with high-resistivity silicon markedly decreases the bulk substrate loss, enabling 2D transmons with time-averaged quality factors (Qavg) of 9.7 × 106 across 45 qubits. For our best qubit, we achieve a Qavg of 1.5 × 107, reaching a maximum Q of 2.5 × 107, corresponding to a lifetime (T1) up to 1.68 ms. This low loss also allows us to observe decoherence effects related to the Josephson junction, and we use an improved, low-contamination junction deposition to achieve Hahn echo coherence times (T2E) exceeding T1. We achieve these materials improvements without any modifications to the qubit architecture, allowing us to readily incorporate standard quantum control gates. We demonstrate single-qubit gates with 99.994% fidelity. The tantalum-on-silicon platform comprises a simple material stack that can potentially be fabricated at the wafer scale and therefore can be readily translated to large-scale quantum processors.

Excited electronic states of fenchone, thiofenchone, and selenofenchone are characterized and assigned with different gas‐phase spectroscopic methods and ab initio quantum chemical calculations. With an increasing atomic number of the chalcogen, increasing bathochromic (red) shifts are observed, which vary in strength for Rydberg states, valence‐excited states, and ionization energies. The spectroscopic insight is used to state‐resolve the contributions in multiphoton photoelectron circular dichroism with femtosecond laser pulses. This is shown to be a sensitive observable of molecular chirality in all studied chalcogenofenchones. This work contributes new spectroscopic information, particularly on thiofenchone and selenofenchone. It may open a perspective for future coherent control experiments exploiting resonances in the visible and near‐ultraviolet spectral regions.

Integrated input system for partially coherent light control in optical neural networks for remote sensing

Abstract We present a theoretical study on the quantum control of ultrafast Rabi dynamics in atoms driven by chirped extreme ultraviolet (XUV) pulses. Motivated by recent experimental advances using free-electron lasers, we derive an analytical solution of the Rabi oscillation under the rotating wave approximation, incorporating the spectral chirp of the XUV field. Within the essential-states model, we demonstrate how the chirp modulates the phase of the excited-state amplitude, inducing an observable asymmetry in the Autler-Townes (AT) doublets of the photoelectrons. Our theoretical predictions, benchmarked against time-dependent Schrödinger equation simulations, reveal that chirp-dependent phase modulation governs the spectral asymmetry, offering a time-domain perspective for interpreting strong-field photoionization at short wavelengths. This work provides a compact analytical framework for chirp-mediated coherent control in the XUV regime and sheds light on recent experimental observations of asymmetric AT structures in helium.

Fluorescent nanodiamonds (FNDs) containing nitrogen-vacancy (NV) defects are useful probes for biological imaging and nanoscale sensing applications. Here, we explore the effect of chemical surface modifications and core-shell structures on the T1 relaxation times of 100 nm FNDs hosting nitrogen-vacancy ensembles. The results show that surface oxidation and silica coating of FNDs using the Stöber method can dramatically increase the spin relaxation time from T1 = 320 ± 9 μs to T1 = 1.00 ± 0.06 ms. Using FT-IR and NEXAFS measurements conducted on air oxidized particles, we find that changes to surface functional groups and sp2 carbon density may be responsible for the observed enhancements to the spin relaxation rate. Finally, we use a Monte Carlo model to numerically investigate the relationship between chemical sensitivity and shell thickness and find that a shell thickness on the order of 1 nm should provide the highest sensitivity. Our findings demonstrate that the surface of FNDs can be engineered to exhibit bulk-like T1 relaxation times, in the absence of complex quantum control sequences, which is crucial to advancing biosensing and imaging applications where surface spin noise currently limits measurement precision.

Abstract Imaging of microwave magnetic fields with nano-scale resolution has interesting applications. Specifically, detecting the orientation of the microwave fields is useful in condensed matter physics and quantum control. However, most of the existing methods for microwave field imaging are limited to detecting the magnitude of the fields. Due to their small sensor size and favorable optical and spin properties, nitrogen-vacancy (NV) centers in diamond are highly suitable for imaging dc and ac magnetic fields. The reported methods for detecting the direction of microwave magnetic fields use pulsed Rabi frequency measurements. Here, we demonstrate imaging of the direction of linearly polarized microwave magnetic fields by only using continuous-wave experiments on NV centers. This simplifies the sensor apparatus and is particularly advantageous in applications where pulsing of the target microwave field is not possible. The method requires static bias magnetic field oriented perpendicular to the quantization axis of NV centers. We detect the direction of an arbitrary microwave magnetic field using NV centers of two different orientations of an NV ensemble. Moreover, we demonstrate that the projection of the microwave fields onto a plane can be imaged using NV centers of single orientation. This can be straightforwardly implemented using a single NV center.

Nonlinear spectroscopies utilizing ultrafast, broadband laser pulses are now widely used techniques for the study of molecular structures, interactions, and dynamics with ever increasing molecular specificity. Broadband laser pulses, however, result in signals produced by many overlapping nonlinear pathways that can be challenging to separate. To overcome this, we introduce a mixed time-frequency domain pulse-shaping approach that uses phase-controlled, Boxcar-frequency-filtered pulses to isolate specific nonlinear pathways in a vibrational action-spectroscopy framework. By filtering each pulse to excite a single normal mode and exploiting narrow transitions of cryogenically cooled gas-phase molecular ions, we selectively prepare and detect rephasing, nonrephasing, and two-quantum coherence pathways, the latter of which provides anharmonic information that is typically inaccessible in action-based nonlinear experiments. This strategy establishes a clear and simplified platform for resolving pathway-specific dynamics, laying the foundation for future studies of higher-order quantum control in complex molecular systems in both gas and condensed phases.

This paper presents a flexible femto-tesla detector design using multi-level cascade modules (quantum magnetic chips, semiconductor cooling, graphene superconductors, power supply, and control circuits). The quantum magnetic chip could be any quantum effect-based chip such as tunnel magnetoresistance, superconducting quantum interference devices, spin exchange relaxation-free, optically pumped magnetometers, semiconductor cooling device could be made of bismuth telluride, lead telluride, silicon–germanium, and bismuth antimonide alloys with copper or graphene coated ceramic plate, soft version is preferable to prevent long term cracking issue, the superconductor could be zero resistance based or Meissner effect based, critical temperature high one is preferable, such as graphene, quasi superconduct like Ohno Continuous Casting (CCC) is acceptable as well, power supply and control circuits must be extreme low noise made with the latest chip technology like silicon carbide and silicon nitride. Such design is mainly meant for educational usage. The lower cost is the main design goal. Its magnetic focusing lens combines semiconductors with room-temperature quasi-superconductors. A tapered superconducting disk with a central elliptical hole concentrates magnetic flux by repelling field lines toward the hole, amplifying field strength. Civilian applications include detecting biological magnetism, say, monitoring the student attention level during the study, diagnosing Alzheimer’s and depression in humans/pets. The high-end military uses involve long-range detection of stealth submarines, carriers, tanks, and stealth aircraft. The main challenge of designing such a system is to understand the environment magnetic noise fluctuation patterns, as such, we have conducted short and long term measurements to catch the effect of Moon cycle on the background noise, these data and analysis will allow us to design an advanced Karman filter to remove the Moon noise, to see femto-Tesla variation in a more accurate design.

Abstract Entanglement is a fundamental resource for many applications in quantum information processing. Here, we investigate how quantum transport in simple quantum graphs, modeled as controlled two-level quantum systems, can be utilized for generating entangled states through coherent control operations between two simple quantum graphs. A controlled operation is defined such that the scattering behavior of one quantum graph dynamically modifies the other. Our analysis reveals the precise conditions under which maximal entanglement or separability arises, including configurations that can be implemented via phase shifts in graph structures. Our findings demonstrate that the maximal entanglement in this system is closely related to recent results on randomized quantum graphs. These results provide new pathways for engineering entanglement using simple quantum graphs and suggest experimental feasibility using microwave networks.

Abstract As we advance towards next-generation quantum technologies characterized by coherence, entanglement, and quantum control, chemistry is emerging as a critical enabler of quantum material innovation. This perspective explores how modern chemical strategies provide atomic-level control over material properties, allowing deterministic design of quantum states and interfaces. We highlight recent advances in spin-active molecules, quantum dots, two-dimensional materials, and hybrid platforms where chemistry shapes coherence, coupling, and device integration. Tools such as coordination chemistry, defect engineering, and surface passivation are shown to directly impact quantum behaviour, while chemical theory and spectroscopy enable deep insight into structure–function relationships. Through case studies ranging from strain-induced Rashba effects to single-atom manipulation, we illustrate how chemistry transcends traditional roles to become a central architect of quantum technologies. We argue for a new paradigm of ‘quantum-informed chemistry’ as essential for designing scalable, high-fidelity systems for quantum sensing, computation, and communication.

Abstract This article examines the legal obligations of third states regarding arms deliveries to Israel in the context of the ongoing armed conflict with Hamas. Special emphasis will be placed on the respective national practices, with a particular focus on the Netherlands and Germany. The legal avenues available to challenge export licenses vary significantly across jurisdictions, with some countries imposing considerably greater procedural hurdles than others. Another critical issue is the reluctance of national courts to intervene in export licensing decisions. This hesitancy stems from the fact that such decisions are deeply intertwined with security policy considerations and are primarily regarded as matters of political discretion. A coherent export control practice that aligns with international law is therefore urgently needed.

Theory of the two-photon Franz-Keldysh effect and electric-field-induced bichromatic coherent control

Excitons in atomically thin transition metal dichalcogenides (TMDs) possess intriguing optical properties, drawing interest for both technology and fundamental research. However, as the demands for nanodevice applications and the exploration of fundamental physics push toward smaller, subwavelength scales, studying them locally is challenging. In this work, we introduce a cryogenic scanning probe photoelectrical sensing technique, termed exciton-resonant microwave impedance microscopy (ER-MIM), to measure the excitonic responses in a monolayer MoSe2 device at 1.5K. From the microwave signal changes, we identify exciton polarons and their Rydberg states. Building on these observations, we systemically reveal the local and nonlocal effects of carrier density, inhomogeneous electric fields, as well as dielectric screening on excitons, beyond the reach of conventional probes. By further integrating deep learning techniques, we precisely extracted the electrical parameters surrounding excitons, demonstrating a quantified, exciton-assisted nanoscale electrometry. Our results provide new insight into exciton-environment interactions, establish ER-MIM as a powerful optoelectronic sensing platform, and open avenues for exciton-based quantum control and device technologies.

Lindblad estimation with fast and precise quantum control

This manuscript explores the coherent control of optical lattices and optical unit cells. Optical lattices are formed by the counter-propagation of Laguerre Gaussian beams within an atomic medium. Variations in absorption and the refractive index along the x and y axes provide insight into the confined modes of the optical lattice and its unit cells, from which we can extract information about mode confinement. Density plots of the absorption spectrum and refractive index reveal the presence of unit cells in both the valley and peak regions of the counter-propagating Laguerre Gaussian standing wave fields. In this manuscript, we control the Wigner and cubic-type unit cells of optical lattices with lattice parameters a=0.3lambda , b=0.3lambda , c=0.3lambda, a=0.5lambda , b=0.5lambda , c=0.5lambda, a=0.6lambda , b=0.6lambda , c=0.6lambda and a=0.2lambda , b=0.2lambda , c=0.2lambda.

Optical skyrmions extend the concept of topological protection from high-energy physics and condensed matter physics to the field of optics, and their unique polarization textures exhibit remarkable potential in numerous domains. However, to date, ultrafast optical skyrmions remain underexplored. This paper proposes a scheme for generating ultrafast optical skyrmion pulses based on a modified self-referenced Sagnac vortex generator. By constructing a Yb:QX crystal passively mode-locked resonator, laser pulses of about 3 ps in both fundamental mode-locked and Q-switched mode-locked states are generated. Combined with a modified Sagnac interferometer with the achromatic property to achieve coherent superposition and polarization control, three types of topological structure ultrafast pulses, namely Néel-type, Bloch-type, and anti-type skyrmion, are generated. By verifying topological integrity via Stokes parameters and enabling dynamic switching of topological types through phase difference adjustment, this experiment resolves wavelength or bandwidth limitations of traditional methods. It thus offers a new pathway for high-resolution material writing and anti-interference optical communication.

Most existing quantum programming languages are based on the quantum circuit model of computation, as higher-level abstractions are particularly challenging to implement—especially ones relating to quantum control flow. The Qunity language, proposed by Voichick et al., offered such an abstraction in the form of a quantum control construct, with great care taken to ensure that the resulting language is still realizable. However, Qunity lacked a working implementation, and the originally proposed compilation procedure was very inefficient, with even simple quantum algorithms compiling to unreasonably large circuits. In this work, we focus on the efficient compilation of high-level quantum control flow constructs, using Qunity as our starting point. We introduce a wider range of abstractions on top of Qunity's core language that offer compelling trade-offs compared to its existing control construct. We create a complete implementation of a Qunity compiler, which converts high-level Qunity code into the quantum assembly language OpenQASM 3. We develop optimization techniques for multiple stages of the Qunity compilation procedure, including both low-level circuit optimizations as well as methods that consider the high-level structure of a Qunity program, greatly reducing the number of qubits and gates used by the compiler.

High-power fiber lasers are powerful tools used in science, industry, and defense. A major roadblock for further power scaling of single-frequency fiber laser amplifiers is stimulated Brillouin scattering. Efforts have been made to mitigate this nonlinear process, but these were mostly limited to single-mode or few-mode fiber amplifiers, which have good beam quality. Here, we explored a highly multimode fiber amplifier in which stimulated Brillouin scattering was greatly suppressed due to a reduction of light intensity in a large fiber core and a broadening of the Brillouin scattering spectrum by multimode excitation. By applying a spatial wavefront shaping technique to the input light of a nonlinear amplifier, the output beam was focused to a diffraction-limited spot. Our multimode fiber amplifier can operate at high power with high efficiency and narrow linewidth, which ensures high coherence. Optical wavefront shaping enables coherent control of multimode laser amplification, with potential applications in coherent beam combining, large-scale interferometry and directed energy delivery.

Abstract This review provides a forward-looking perspective on chip-scale quantum sensors based on integrated silicon carbide (SiC) photonic platforms. Although SiC quantum sensors, which utilize atomic point defects such as silicon vacancies and divacancies, are powerful tools for nanosensing, their performance in bulk-material configurations is often limited by factors such as poor photon collection and inefficient optical control. The novelty of this work lies in its focused analysis of how SiC photonic integration-leveraging components such as as waveguides, resonators, and metasurfaces can overcome these fundamental limitations. We explore how these integrated platforms enhance light-matter interactions, boost readout fidelity, and enable precise control over quantum states, providing a direct pathway to surpass the sensitivity of current bulk-material sensors. By synthesizing recent breakthroughs in SiC photonics with advances in materials science and quantum control, we outline a scalable road-map for developing high-performance, wafer-deployable quantum sensing systems for applications ranging from biomedical imaging to navigation in harsh environments.