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Journal articleLi Y, Broughton JJ, Tisch JWG, 2025,
Temporal compression of Yb-doped laser pulses in cascaded gas-filled hollow fibers
, OPTICS CONTINUUM, Vol: 4, Pages: 1732-1743 -
Journal articleLatacz BM, Erlewein SR, Fleck M, et al., 2025,
Coherent spectroscopy with a single antiproton spin
, Nature, Vol: 644, Pages: 64-68, ISSN: 0028-0836Coherent quantum transition spectroscopy is a powerful tool in metrology¹, quantum information processing², magnetometry³, and precision tests of the Standard Model⁴. It was applied with great success in proton and deuteron magnetic moment measurements⁵, which culminated in MASER spectroscopy with sub-parts per trillion resolution⁶ and many other experiments at the forefront of physics⁷. All these experiments were performed on macroscopic ensembles of particles, while the coherent spectroscopy of a “free” single nuclear spin has never been reported before. Here, we demonstrate coherent quantum transition spectroscopy of the spin of a single antiproton stored in a cryogenic Penning-trap system. We apply a multi-trap technique⁸, detect the antiproton spin-state using the continuous Stern-Gerlach-effect⁹, and transport the particle to the homogeneous magnetic field of a precision trap (PT). Here, we induce the coherent dynamics and analyze the result by quantum-projection measurements in the analysis trap¹⁰ . We observe for the first time Rabi-oscillations of an antiproton spin and achieve in time-series measurements spin inversion probabilities above 80% at spin coherence times of ≈ 50s. Scans of single-particle spin resonances show inversions >70%, at transition line-widths 16 times narrower than in previous measurements⁸, limited by cyclotron frequency measurement decoherence. This achievement marks a major step towards at least 10-fold improved tests of matter/antimatter symmetry using proton and antiproton magnetic moments.
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Journal articleHaug T, Aolita L, Kim MS, 2025,
Probing quantum complexity via universal saturation of stabilizer entropies
, Quantum, Vol: 9, Pages: 1801-1801, ISSN: 2521-327XNonstabilizerness or `magic' is a key resource for quantum computing and a necessary condition for quantum advantage. Non-Clifford operations turn stabilizer states into resourceful states, where the amount of nonstabilizerness is quantified by resource measures such as stabilizer Rényi entropies (SREs). Here, we show that SREs saturate their maximum value at a critical number of non-Clifford operations. Close to the critical point SREs show universal behavior. Remarkably, the derivative of the SRE crosses at the same point independent of the number of qubits and can be rescaled onto a single curve. We find that the critical point depends non-trivially on Rényi index α. For random Clifford circuits doped with T-gates, the critical T-gate density scales independently of α. In contrast, for random Hamiltonian evolution, the critical time scales linearly with qubit number for α>1, while it is a constant for α<1. This highlights that α-SREs reveal fundamentally different aspects of nonstabilizerness depending on α: α-SREs with α<1 relate to Clifford simulation complexity, while α>1 probe the distance to the closest stabilizer state and approximate state certification cost via Pauli measurements. As technical contributions, we observe that the Pauli spectrum of random evolution can be approximated by two highly concentrated peaks which allows us to compute its SRE. Further, we introduce a class of random evolution that can be expressed as random Clifford circuits and rotations, where we provide its exact SRE. Our results opens up new approaches to characterize the complexity of quantum systems.
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Journal articleLi Z, Solomons NR, Bulmer JFF, et al., 2025,
A complexity transition in displaced Gaussian Boson sampling
, npj Quantum Information, Vol: 11, ISSN: 2056-6387Gaussian Boson Sampling (GBS) is the problem of sampling from the output of photon-number-resolving measurements of squeezed states input to a linear optical interferometer. For purposes of demonstrating quantum computational advantage as well as practical applications,a large photon number is often desirable. However, producing squeezed states with high photon numbers is experimentally challenging. In this work, we examine the computational complexity implications of increasing the photon number by introducing coherent states. This displaces the state in phase space and as such we call this modified problem Displaced GBS. By utilising a connection to the matching polynomial in graph theory, we first describe an efficient classical algorithm for Displaced GBS when displacement is high or when the output state is represented by a non-negative graph. Then we provide complexity theoretic arguments for the quantum advantage of the problem in the low-displacement regime and numerically quantify where the complexity transition occurs.
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Journal articleVylegzhanin A, Brown DJ, Kornovan DF, et al., 2025,
Towards a fictitious magnetic field trap for both ground and Rydberg state <SUP>87</SUP>Rb atoms via the evanescent field of an optical nanofiber
, NEW JOURNAL OF PHYSICS, Vol: 27, ISSN: 1367-2630 -
Journal articleBressanini G, Seron B, Novo L, et al., 2025,
Binned-detector probability distributions for Gaussian boson sampling validation
, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 112, ISSN: 1050-2947Gaussian boson sampling (GBS), a computational problem conjectured to be hard to simulate on a classical machine, has been at the forefront of recent years' experimental and theoretical efforts to demonstrate quantum advantage. The classical intractability of the sampling task makes validating these experiments a challenging and essential undertaking. In this paper, we propose binned-detector probability distributions as a suitable quantity to statistically validate GBS experiments employing photon-number-resolving detectors. We develop the theoretical framework to compute such distributions by leveraging their connection with their respective characteristic function. The latter may be efficiently and analytically computed for squeezed input states as well as for relevant classical hypothesis like squashed states. Our theoretical framework encompasses other validation methods based on marginal distributions and correlation functions. Additionally, it can analytically accommodate various sources of noise, such as losses and partial distinguishability, a feature that has received limited attention within the GBS framework so far. We also derive how binned-detector probability distributions behave when Haar averaged over all possible interferometric networks, extending known results for Fock boson sampling.
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Journal articleLi Z, Kendall MJH, Machado GJ, et al., 2025,
Boosting photon-number-resolved detection rates of transition-edge sensors by machine learning
, Optica Quantum, Vol: 3, Pages: 246-246, ISSN: 2837-6714Transition-edge sensors (TESs) are very effective photon-number-resolving (PNR) detectors that have enabled many photonic quantum technologies. However, their relatively slow thermal recovery time severely limits their operation rate in experimental scenarios compared with leading non-PNR detectors. In this work, we develop an algorithmic approach that enables TESs to detect and accurately classify photon pulses without waiting for a full recovery time between detection events. We propose two machine-learning-based signal processing methods: one supervised learning method and one unsupervised clustering method. By benchmarking against data obtained using coherent states and squeezed states, we show that the methods extend the TES operation rate to 800 kHz, achieving at least a four-fold improvement, whilst maintaining accurate photon-number assignment up to at least five photons. Our algorithms will find utility in applications where high rates of PNR detection are required and in technologies that demand fast active feed-forward of PNR detection outcomes.
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Journal articleMaslennikov DR, Maimaris M, Ning H, et al., 2025,
Interplay between Mixed and Pure Exciton States Controls Singlet Fission in Rubrene Single Crystals
, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 147, Pages: 23536-23544, ISSN: 0002-7863 -
Journal articleHo CJ, Fischer SM, Martirosyan G, et al., 2025,
Joule expansion of a quantum gas
, PHYSICAL REVIEW RESEARCH, Vol: 7 -
Journal articleCheng MH, Khosla KE, Self CN, et al., 2025,
Clifford circuit initialization for variational quantum algorithms
, Physical Review A, Vol: 111, ISSN: 2469-9926We present an initialization method for variational quantum algorithms applicable to intermediate-scale quantum computers. The method explores the efficiently classically simulable Clifford points of a parameterized quantum circuit, using simulated annealing to find a low-energy initial state. We provide numerical evidence of the effectiveness of the technique for different choices of the Hamiltonian structure, number of qubits, and circuit depth. While a number of problems are considered, we note that the method is particularly useful for quantum chemistry problems, for which it is able to capture long-range correlation energy. The presented method could help achieve a quantum advantage in noisy or fault-tolerant intermediate-scale devices by preparing a high-quality initial state.
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Journal articleEtrych J, Martirosyan G, Cao A, et al., 2025,
Universal Quantum Dynamics of Bose Polarons
, PHYSICAL REVIEW X, Vol: 15, ISSN: 2160-3308- Cite
- Citations: 6
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Journal articleLeonhardt M, Schweitzer S, Abbass F, et al., 2025,
Proton transport from the antimatter factory of CERN
, Nature, ISSN: 0028-0836Precision measurements using low-energy antiprotons, exclusively available at the antimatter factory (AMF) of CERN1, offer stringent tests of charge–parity–time (CPT) invariance, which is a fundamental symmetry in the Standard Model of particle physics2. These tests have been realized, for example, in antiprotonic helium3 and antihydrogen4. In our cryogenic Penning-trap experiments5, we measure the magnetic moments6,7 and charge-to-mass ratios of protons and antiprotons and now provide the most precise test of CPT invariance in the baryon sector8. Our experiments are limited by magnetic field fluctuations imposed by the decelerators in the AMF; therefore, we are advancing the relocation of antiprotons to dedicated precision laboratories. Here we present the successful transport of a trapped proton cloud from the AMF using BASE-STEP9—a transportable, superconducting, autonomous and open Penning-trap system that can distribute antiprotons into other experiments. We transferred the trapped protons from our experimental area at the AMF onto a truck and transported them across the Meyrin site of CERN, demonstrating autonomous operation without external power for 4 h and loss-free proton relocation. We thereby confirm the feasibility of transferring particles into low-noise laboratories in the vicinity of the AMF and of using a power generator on the truck10 to reach laboratories throughout Europe. This marks the potential start of a new era in precision antimatter research, enabling low-noise measurements of antiprotons, the charged antimatter ions H+11 and H-2 (ref. 12), and other accelerator-produced ions, such as hydrogen-like lead or uranium ions13,14.
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Journal articleLi H, Xie J, Kwon H, et al., 2025,
Experimental demonstration of generalized quantum fluctuation theorems in the presence of coherence
, Science Advances, Vol: 11, ISSN: 2375-2548Fluctuation theorems have elevated the second law of thermodynamics to a statistical realm by establishing a connection between time-forward and time-reversal probabilities, providing invaluable insight into nonequilibrium dynamics. While well established in classical systems, their quantum generalization, incorporating coherence and the diversity of quantum noise, remains open. We report the experimental validation of a quantum fluctuation theorem (QFT) in a photonic system, applicable to general quantum processes with nonclassical characteristics, including quasi-probabilistic descriptions of entropy production and multiple time-reversal processes. Our experiment confirms that the ratio between the quasi-probabilities of the time-forward and any multiple time-reversal processes obeys a generalized Crooks QFT. Moreover, coherence induced by a quantum process leads to the imaginary components of quantum entropy production, governing the phase factor in the QFT. These findings underscore the fundamental symmetry between a general quantum process and its time reversal, providing an elementary toolkit to explore noisy quantum information processing.
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Journal articleAlexander O, Ayuso D, Matthews M, et al., 2025,
Attosecond physics and technology
, APPLIED PHYSICS LETTERS, Vol: 126, ISSN: 0003-6951- Cite
- Citations: 1
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Journal articleMorris SJ, Ho CJ, Fischer SM, et al., 2025,
Scaling laws governing the collapse of a Bose-Einstein condensate
, PHYSICAL REVIEW A, Vol: 111, ISSN: 2469-9926- Cite
- Citations: 1
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Journal articleAbdalla A, Abe M, Abend S, et al., 2025,
Terrestrial Very-Long-Baseline Atom Interferometry: summary of the second workshop
, EPJ Quantum Technology, Vol: 12, ISSN: 2196-0763This summary of the second Terrestrial Very-Long-Baseline Atom Interferometry (TVLBAI) Workshop provides a comprehensive overview of our meeting held in London in April 2024 (Second Terrestrial Very-Long-Baseline Atom Interferometry Workshop, Imperial College, April 2024), building on the initial discussions during the inaugural workshop held at CERN in March 2023 (First Terrestrial Very-Long-Baseline Atom Interferometry Workshop, CERN, March 2023). Like the summary of the first workshop (Abend et al. in AVS Quantum Sci. 6:024701, 2024), this document records a critical milestone for the international atom interferometry community. It documents our concerted efforts to evaluate progress, address emerging challenges, and refine strategic directions for future large-scale atom interferometry projects. Our commitment to collaboration is manifested by the integration of diverse expertise and the coordination of international resources, all aimed at advancing the frontiers of atom interferometry physics and technology, as set out in a Memorandum of Understanding signed by over 50 institutions (Memorandum of Understanding for the Terrestrial Very Long Baseline Atom Interferometer Study).
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Journal articleThielemann F, Siemund J, von Schoenfeld D, et al., 2025,
Exploring Atom-Ion Feshbach Resonances below the s-Wave Limit
, PHYSICAL REVIEW X, Vol: 15, ISSN: 2160-3308- Cite
- Citations: 4
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Journal articleAthanasakis-Kaklamanakis M, Wilkins SG, Skripnikov LV, et al., 2025,
Electron correlation and relativistic effects in the excited states of radium monofluoride
, NATURE COMMUNICATIONS, Vol: 16- Cite
- Citations: 4
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Journal articleAllegre H, Broughton JJ, Klee T, et al., 2025,
Extension of high-harmonic generation cutoff in solids to 50 eV using MgO
, OPTICS LETTERS, Vol: 50, Pages: 1492-1495, ISSN: 0146-9592- Cite
- Citations: 1
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Journal articleKlee T, Mukherjee R, Broughton JJ, et al., 2025,
Bayesian optimization of resonant dispersive wave generation in hollow capillary fibers
, Optics Express, Vol: 33, ISSN: 1094-4087Resonant dispersive wave (RDW) generation in hollow capillary fibers (HCFs) is a powerful technique for producing ultrashort light pulses in the deep ultraviolet range, which are important for ultrafast spectroscopy and material processing. However, the complex nonlinear dynamics governing this process and the large associated parameter space make it challenging to achieve optimal RDW pulses with the highest peak power. In this study, Bayesian optimization (BO) is coupled with the open source Luna.jl simulation framework to optimize the HCF and pump pulse paramters for less than 5 femtosecond (fs) RDW generation at a target wavelength of 200 nm. Temporally non-structured RDW were consistently identified with peak powers of up to 14 GW, exceeding experimentally published values by up to 70 %. Furthermore, a subset of the RDW optima exhibited an energy stability that is better than that of the pump pulse. Given that this approach can be generalized to other RDW wavelengths, our findings suggest that BO is a valuable tool in developing HCF systems that support RDW generation tailored to a particular experimental need.
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Journal articleClarke J, Cryer-Jenkins EA, Gupta A, et al., 2025,
Theoretical framework for enhancing or enabling cooling of a mechanical resonator via the anti-Stokes or Stokes interaction and zero-photon detection
, PHYSICAL REVIEW A, Vol: 111, ISSN: 2469-9926 -
Journal articleCryer-Jenkins EA, Major KD, Clarke J, et al., 2025,
Enhanced Laser Cooling of a Mechanical Resonator via Zero-Photon Detection
, PHYSICAL REVIEW LETTERS, Vol: 134, ISSN: 0031-9007 -
Journal articleSun J, Vilchez-Estevez L, Vedral V, et al., 2025,
Probing spectral features of quantum many-body systems with quantum simulators
, NATURE COMMUNICATIONS, Vol: 16- Cite
- Citations: 6
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Journal articleWang Y, Rodewald J, Lopez O, et al., 2025,
Wavelength modulation laser spectroscopy of N<sub>2</sub>O at 17 <i>μ</i>m
, NEW JOURNAL OF PHYSICS, Vol: 27, ISSN: 1367-2630- Cite
- Citations: 1
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Journal articleWang J, Driver T, Franz PL, et al., 2025,
Probing Electronic Coherence between Core-Level Vacancies at Different Atomic Sites
, PHYSICAL REVIEW X, Vol: 15, ISSN: 2160-3308 -
Journal articleWang P, Kwon H, Luan C-Y, et al., 2025,
Snapshotting quantum dynamics at multiple time points (vol 15, 8900, 2024)
, NATURE COMMUNICATIONS, Vol: 16 -
Conference paperWhite AD, Ainsworth A, Bahra D, et al., 2025,
Quantum Sensing for Rail Positioning
Global navigation satellite systems (GNSS) are critical to our daily lives and underpin numerous sectors including transport, finance, and defence. The estimated financial impact of GNSS failure for the UK is over £1bn per day [1]. In areas where GNSS cannot be used, inertial navigation provides an alternative to accurately position vehicles. For many applications, the drift in the classical accelerometers and gyroscopes that underpin inertial navigation systems limits the position accuracy that can be achieved.
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Journal articleCryer-Jenkins E, Leung A, Rathee H, et al., 2025,
Brillouin-Mandelstam scattering in telecommunications optical fiber at millikelvin temperatures
, APL Photonics, Vol: 10, ISSN: 2378-0967Brillouin–Mandelstam scattering is a strong and readily accessible optical nonlinearity, enabling a wide array of applications and research directions. For instance, the three-wave mixing process has been employed to great success in narrow-linewidth lasers, sensing applications, microscopy, and signal processing. While most of these avenues focus on room temperature operation, there is now increasing interest in cryogenic operation owing to the scattering mechanism’s significant potential for applications and fundamental physics at low temperatures. Here, we measure the Brillouin scattering spectrum in standard single-mode telecommunication optical fibers at millikelvin temperatures using a closed-cycle dilution refrigerator and optical heterodyne detection. Our experiments are performed with a cryostat temperature from 50 mK to 27 K, extending previously reported measurements that utilized liquid helium-4 cryostats with temperatures greater than 1 K. At millikelvin temperatures, our experiment observes coherent acoustic interactions with microscopic defects in the amorphous material—two-level-systems (TLSs)—which has not been previously observed in optical fibers. The measured behavior of the linewidth with temperature is in agreement with the well-established models of ultrasonic attenuation in amorphous materials comprising a background intrinsic scattering, thermally activated scattering, and incoherent and coherent TLS interactions. This work provides a foundation for a wide range of applications and further research, including sensing applications, new approaches to investigate TLS physics, and Brillouin-scattering-based quantum science and technology.
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Conference paperRowley M, Webber-Date A, Osborn PF, et al., 2025,
A Quantum-classical cold atom system for inertial navigation
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Conference paperWhite AD, Ainsworth A, Bahra D, et al., 2025,
Quantum Sensing for Rail Positioning
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