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  • Journal article
    Mok WK, Zhang H, Haug T, Luo X, Lo GQ, Li Z, Cai H, Kim MS, Liu AQ, Kwek LCet al., 2024,

    Rigorous noise reduction with quantum autoencoders

    , AVS Quantum Science, Vol: 6

    Reducing noise in quantum systems is a significant challenge in advancing quantum technologies. We propose and demonstrate a noise reduction scheme utilizing a quantum autoencoder, which offers rigorous performance guarantees. The quantum autoencoder is trained to compress noisy quantum states into a latent subspace and eliminate noise through projective measurements. We identify various noise models in which the noiseless state can be perfectly reconstructed, even at high noise levels. We apply the autoencoder to cool thermal states to the ground state and reduce the cost of magic state distillation by several orders of magnitude. Our autoencoder can be implemented using only unitary transformations without the need for ancillas, making it immediately compatible with state-of-the-art quantum technologies. We experimentally validate our noise reduction methods in a photonic integrated circuit. Our results have direct applications in enhancing the robustness of quantum technologies against noise.

  • Journal article
    Popa S, Schaller S, Fielicke A, Lim J, Sartakov BG, Tarbutt MR, Meijer Get al., 2024,

    Understanding Inner-Shell Excitations in Molecules through Spectroscopy of the <mml:math xmlns:mml="" display="inline"><mml:mn>4</mml:mn><mml:mi>f</mml:mi></mml:math> Hole States of YbF

    , Physical Review X, Vol: 14

    <jats:p>Molecules containing a lanthanide atom have sets of electronic states arising from excitation of an inner-shell electron. These states have received little attention but are thought to play an important role in laser cooling of such molecules and may be a useful resource for testing fundamental physics. We study a series of inner-shell excited states in YbF using resonance-enhanced multiphoton ionization spectroscopy. We investigate the excited states of lowest energy, 8474, 9013, and <a:math xmlns:a="" display="inline"><a:mn>9090</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:msup><a:mrow><a:mi>cm</a:mi></a:mrow><a:mrow><a:mo>−</a:mo><a:mn>1</a:mn></a:mrow></a:msup></a:math> above the ground state, all corresponding to the configuration <c:math xmlns:c="" display="inline"><c:mrow><c:mn>4</c:mn><c:msup><c:mrow><c:mi>f</c:mi></c:mrow><c:mrow><c:mn>13</c:mn></c:mrow></c:msup><c:mn>6</c:mn><c:msup><c:mrow><c:mi>s</c:mi></c:mrow><c:mrow><c:mn>2</c:mn></c:mrow></c:msup><c:mtext> </c:mtext><c:mtext> </c:mtext><c:msub><c:mrow><c:mmultiscripts><c:mrow><c:mi>F</c:mi></c:mrow><c:mprescripts/><c:none/><c:mrow><c:mn>2</c:mn></c:mrow></c:mmultiscripts></c:mrow><c:mrow><c:mn>7</c:mn><c:mo>/</c:mo><c:mn>2</c:mn></c:mrow></c:msub></c:mrow></c:math> of the <e:math xmlns:e="" display="inline"><e:mrow><e:msup>&l

  • Journal article
    Walraven EF, Tarbutt MR, Karman T, 2024,

    Scheme for deterministic loading of laser-cooled molecules into optical tweezers

    , Physical Review Letters, Vol: 132, ISSN: 0031-9007

    We propose to repeatedly load laser-cooled molecules into optical tweezers, and transfer them to storage states that are rotationally excited by two additional quanta. Collisional loss of molecules in these storage states is suppressed, and a dipolar blockade prevents the accumulation of more than one molecule. Applying three cycles loads tweezers with single molecules at an 80% success rate, limited by residual collisional loss. This improved loading efficiency reduces the time needed for rearrangement of tweezer arrays, which would otherwise limit the scalability of neutral molecule quantum computers.

  • Journal article
    Cornish SL, Tarbutt MR, Hazzard KRA, 2024,

    Quantum computation and quantum simulation with ultracold molecules

    , Nature Physics, Vol: 20, Pages: 730-740, ISSN: 1745-2473

    Ultracold molecules confined in optical lattices or tweezer traps can be used to process quantum information and simulate the behaviour of many-body quantum systems. Molecules offer several advantages for these applications. They have a large set of stable states with strong transitions between them and long coherence times. Molecules can be prepared in a chosen state with high fidelity, and the state populations can be measured efficiently. Control over their long-range dipole–dipole interactions can enable the entanglement of pairs of molecules, generating interesting and technologically useful many-body states. This Review covers the advances made so far in the field of quantum simulation and computation with ultracold molecules and the challenges still to overcome.

  • Journal article
    Popa S, Schaller S, Fielicke A, Lim J, Sartakov BG, Tarbutt M, Meijer Get al., 2024,

    Understanding inner-shell excitations in molecules through spectroscopy of the 4f hole states of YbF

    , Physical Review X, Vol: 14, ISSN: 2160-3308

    Molecules containing a lanthanide atom have sets of electronic states arising from excitation of an inner-shell electron. These states have received little attention, but are thought to play an important role in laser cooling of such molecules and may be a useful resource for testing fundamental physics. We study a series of inner-shell excited states in YbF using resonance-enhanced multi-photon ionisation spectroscopy. We investigate the excited states of lowest energy, 8474, 9013 and 9090 cm⁻¹ above the ground state, all corresponding to the configuration 4f¹³6s² ²F₇⁄₂ of the Yb⁺ ion. They are metastable, since they have no electric dipole allowed transitions to the ground state. We also characterize a state at 31050 cm¯¹ that is easily excited from both the ground and metastable states, which makes it especially useful for this spectroscopic study. Finally, we study two states at 48720 cm¯¹ and 48729 cm¯¹, which are above the ionization limit and feature strong auto-ionizing resonances that prove useful for efficient detection of the molecules and for identifying the rotational quantum number of each line in the spectrum. We resolve the rotational structures of all these states and find that they can all be described by a very simple model based on Hund’s case (c). Our study provides information necessary for laser slowing and magneto-optical trapping of YbF, which is an important species for testing fundamental physics. We also consider whether the low-lying inner-shell states may themselves be useful as probes of the electron’s electric dipole moment or of varying fundamental constants, since they are long-lived states in a laser-coolable molecule featuring closely-spaced levels of opposite parity.

  • Journal article
    Cheng C, Frasinski LJ, Moǧol G, Allum F, Howard AJ, Bucksbaum PH, Forbes R, Weinacht Tet al., 2024,

    Multiparticle cumulant mapping for Coulomb explosion imaging: Calculations and algorithm

    , Physical Review A, Vol: 109, ISSN: 2469-9926

    We present a versatile cumulant mapping algorithm for analyzing correlated particle emission, offering insights into complex electronic and nuclear dynamics. Recently, we have demonstrated the use of cumulant mapping to extract information-rich correlations between the momenta of multiple fragments produced in Coulomb explosion imaging experiments [C. Cheng, Phys. Rev. Lett. 130, 093001 (2023)0031-900710.1103/PhysRevLett.130.093001]. We define cumulant mapping in terms of histograms, enabling fast computation of linear (additive) observables. However, applying the same algorithm to nonlinear (nonadditive) observables poses challenges, as the computation time of conventional estimators scales nonlinearly with data size. To overcome this, we develop estimators and an accompanying algorithm to enable computationally efficient estimation of the cumulant of interest. Comparisons of computation times and signal-to-noise ratios reveal the superior performance of our approach. This method is demonstrated on the (D+, D+, C+, O+) dissociation channel of CD2O4+ produced in a strong-field ionization experiment. Additionally, Poisson statistics are used to simulate the two methods and provide insights into the efficiency of our algorithm. The proposed methodology unlocks efficient computation of cumulant mapping for a broader range of complex systems and observables, such as the laser pulse dependence of ionization dynamics.

  • Journal article
    Thomas SE, Wagner L, Joos R, Sittig R, Nawrath C, Burdekin P, de Buy Wenniger IM, Rasiah MJ, Huber-Loyola T, Sagona-Stophel S, Höfling S, Jetter M, Michler P, Walmsley IA, Portalupi SL, Ledingham PMet al., 2024,

    Deterministic storage and retrieval of telecom light from a quantum dot single-photon source interfaced with an atomic quantum memory

    , Science Advances, Vol: 10, ISSN: 2375-2548

    A hybrid interface of solid-state single-photon sources and atomic quantum memories is a long sought-after goal in photonic quantum technologies. Here, we demonstrate deterministic storage and retrieval of light from a semiconductor quantum dot in an atomic ensemble quantum memory at telecommunications wavelengths. We store single photons from an indium arsenide quantum dot in a high-bandwidth rubidium vapor-based quantum memory, with a total internal memory efficiency of (12.9 ± 0.4)%. The signal-to-noise ratio of the retrieved light field is 18.2 ± 0.6, limited only by detector dark counts.

  • Journal article
    Alaa El-Din K, Alexander O, Frasinski L, Mintert F, Guo Z, Duris J, Zhang Z, Cesar D, Franz P, Driver T, Walter P, Cryan J, Marinelli A, Marangos J, Mukherjee Ret al., 2024,

    Efficient prediction of attosecond two-colour pulses from an X-ray free-electron laser with machine learning

    , Scientific Reports, Vol: 14, ISSN: 2045-2322

    X-ray free-electron lasers are sources of coherent, high-intensity X-rays with numerous applications in ultra-fast measurements and dynamic structural imaging. Due to the stochastic nature of the self-amplified spontaneous emission process and the difficulty in controlling injection of electrons, output pulses exhibit significant noise and limited temporal coherence. Standard measurement techniques used for characterizing two-coloured X-ray pulses are challenging, as they are either invasive or diagnostically expensive. In this work, we employ machine learning methods such as neural networks and decision trees to predict the central photon energies of pairs of attosecond fundamental and second harmonic pulses using parameters that are easily recorded at the high-repetition rate of a single shot. Using real experimental data, we apply a detailed feature analysis on the input parameters while optimizing the training time of the machine learning methods. Our predictive models are able to make predictions of central photon energy for one of the pulses without measuring the other pulse, thereby leveraging the use of the spectrometer without having to extend its detection window. We anticipate applications in X-ray spectroscopy using XFELs, such as in time-resolved X-ray absorption and photoemission spectroscopy, where improved measurement of input spectra will lead to better experimental outcomes.

  • Journal article
    Yu S, Liu W, Tao S-J, Li Z-P, Wang Y-T, Zhong Z-P, Patel RB, Meng Y, Yang Y-Z, Wang Z-A, Guo N-J, Zeng X-D, Chen Z, Xu L, Zhang N, Liu X, Yang M, Zhang W-H, Zhou Z-Q, Xu J-S, Tang J-S, Han Y-J, Li C-F, Guo G-Cet al., 2024,

    A von-Neumann-like photonic processor and its application in studying quantum signature of chaos.

    , Light Sci Appl, Vol: 13

    Photonic quantum computation plays an important role and offers unique advantages. Two decades after the milestone work of Knill-Laflamme-Milburn, various architectures of photonic processors have been proposed, and quantum advantage over classical computers has also been demonstrated. It is now the opportune time to apply this technology to real-world applications. However, at current technology level, this aim is restricted by either programmability in bulk optics or loss in integrated optics for the existing architectures of processors, for which the resource cost is also a problem. Here we present a von-Neumann-like architecture based on temporal-mode encoding and looped structure on table, which is capable of multimode-universal programmability, resource-efficiency, phase-stability and software-scalability. In order to illustrate these merits, we execute two different programs with varying resource requirements on the same processor, to investigate quantum signature of chaos from two aspects: the signature behaviors exhibited in phase space (13 modes), and the Fermi golden rule which has not been experimentally studied in quantitative way before (26 modes). The maximal program contains an optical interferometer network with 1694 freely-adjustable phases. Considering current state-of-the-art, our architecture stands as the most promising candidate for real-world applications.

  • Journal article
    Tang H, Shang X-W, Shi Z-Y, He T-S, Feng Z, Wang T-Y, Shi R, Wang H-M, Tan X, Xu X-Y, Wang Y, Gao J, Kim MS, Jin X-Met al., 2024,

    Simulating photosynthetic energy transport on a photonic network

    , npj Quantum Information, Vol: 10, ISSN: 2056-6387

    Quantum effects in photosynthetic energy transport in nature, especially for the typical Fenna-Matthews-Olson (FMO) complexes, are extensively studied in quantum biology. Such energy transport processes can be investigated as open quantum systems that blend the quantum coherence and environmental noise, and have been experimentally simulated on a few quantum devices. However, the existing experiments always lack a solid quantum simulation for the FMO energy transport due to their constraints to map a variety of issues in actual FMO complexes that have rich biological meanings. Here we successfully map the full coupling profile of the seven-site FMO structure by comprehensive characterisation and precise control of the evanescent coupling of the three-dimensional waveguide array. By applying a stochastic dynamical modulation on each waveguide, we introduce the base site energy and the dephasing term in coloured noise to faithfully simulate the power spectral density of the FMO complexes. We show our photonic model well interprets the phenomena including reorganisation energy, vibrational assistance, exciton transfer and energy localisation. We further experimentally demonstrate the existence of an optimal transport efficiency at certain dephasing strength, providing a window to closely investigate environment-assisted quantum transport.

  • Journal article
    Stray B, Ennis O, Hedges S, Dey S, Langlois M, Bongs K, Lellouch S, Holynski M, Bostwick B, Chen J, Eyler Z, Gibson V, Harte TL, Hsu CC, Karzazi M, Mitchell J, Mouelle N, Schneider U, Tang Y, Tkalcec K, Zhi Y, Clarke K, Vick A, Bridges K, Coleman J, Elertas G, Hawkins L, Hindley S, Hussain K, Metelko C, Throssell H, Baynham CFA, Buchmüller O, Evans D, Hobson R, Iannizzotto-Venezze L, Josset A, Pasatembou E, Sauer BE, Tarbutt MR, Badurina L, Beniwal A, Blas D, Carlton J, Ellis J, McCabe C, Bentine E, Booth M, Bortoletto D, Foot C, Gómez-Monedero Castellanos CM, Hird T, Hughes K, James A, Lowe A, March-Russell J, Schelfhout J, Shipsey I, Weatherill D, Wood D, Balashov S, Bason MG, Boehm J, Courthold M, van der Grinten M, Majewski P, Marchant AL, Newbold D, Pan Z, Tam Z, Valenzuela T, Wilmut Iet al., 2024,

    Centralized design and production of the ultra-high vacuum and laser-stabilization systems for the AION ultra-cold strontium laboratories

    , AVS Quantum Science, Vol: 6, ISSN: 2639-0213

    This paper outlines the centralized design and production of the ultra-high-vacuum sidearm and laser-stabilization systems for the AION Ultra-Cold Strontium Laboratories. Commissioning data on the residual gas and steady-state pressures in the sidearm chambers, on magnetic field quality, on laser stabilization, and on the loading rate for the 3D magneto-optical trap are presented. Streamlining the design and production of the sidearm and laser stabilization systems enabled the AION Collaboration to build and equip in parallel five state-of-the-art Ultra-Cold Strontium Laboratories within 24 months by leveraging key expertise in the collaboration. This approach could serve as a model for the development and construction of other cold atom experiments, such as atomic clock experiments and neutral atom quantum computing systems, by establishing dedicated design and production units at national laboratories.

  • Journal article
    Schwickert D, Przystawik A, Diaman D, Kip D, Marangos JP, Laarmann Tet al., 2024,

    Coupled electron-nuclear dynamics induced and monitored with femtosecond soft X-ray pulses in the amino acid glycine

    , The Journal of Physical Chemistry A: Isolated Molecules, Clusters, Radicals, and Ions; Environmental Chemistry, Geochemistry, and Astrochemistry; Theory, Vol: 128, Pages: 989-995, ISSN: 1089-5639

    The coupling of electronic and nuclear motion in polyatomic molecules is at the heart of attochemistry. The molecular properties, transient structures, and reaction mechanism of these many-body quantum objects are defined on the level of electrons and ions by molecular wave functions and their coherent superposition, respectively. In the present contribution, we monitor nonadiabatic quantum wave packet dynamics during molecular charge motion by reconstructing both the oscillatory charge density distribution and the characteristic time-dependent nuclear configuration coordinate from time-resolved Auger electron spectroscopic data recorded in previous studies on glycine molecules [Schwickert et al. Sci. Adv. 2022, 8, eabn6848]. The electronic and nuclear motion on the femtosecond time scale was induced and probed in kinematically complete soft X-ray experiments at the FLASH free-electron laser facility. The detailed analysis of amplitude, instantaneous phase, and instantaneous frequency of the propagating many-body wave packet during its lifecycle provides unprecedented insight into dynamical processes beyond the Born-Oppenheimer approximation. We are confident that the refined experimental data evaluation helps to develop new theoretical tools to describe time-dependent molecular wave functions in complicated but ubiquitous non-Born-Oppenheimer photochemical conditions.

  • Journal article
    Fekete J, Joshi P, Barrett TJ, James TM, Shah R, Gadge A, Bhumbra S, Evans W, Tripathi M, Large M, Dalton AB, Oručević F, Krüger Pet al., 2024,

    Quantum Gas-Enabled Direct Mapping of Active Current Density in Percolating Networks of Nanowires.

    , Nano Lett, Vol: 24, Pages: 1309-1315

    Electrically percolating nanowire networks are among the most promising candidates for next-generation transparent electrodes. Scientific interest in these materials stems from their intrinsic current distribution heterogeneity, leading to phenomena like percolating pathway rerouting and localized self-heating, which can cause irreversible damage. Without an experimental technique to resolve the current distribution and an underpinning nonlinear percolation model, one relies on empirical rules and safety factors to engineer materials. We introduce Bose-Einstein condensate microscopy to address the longstanding problem of imaging active current flow in 2D materials. We report on performance improvement of this technique whereby observation of dynamic redistribution of current pathways becomes feasible. We show how this, combined with existing thermal imaging methods, eliminates the need for assumptions between electrical and thermal properties. This will enable testing and modeling individual junction behavior and hot-spot formation. Investigating both reversible and irreversible mechanisms will contribute to improved performance and reliability of devices.

  • Journal article
    Xu L, Zhou M, Tao R, Zhong Z, Wang B, Cao Z, Xia H, Wang Q, Zhan H, Zhang A, Yu S, Xu N, Dong Y, Ren C, Zhang Let al., 2024,

    Resource-Efficient Direct Characterization of General Density Matrix.

    , Phys Rev Lett, Vol: 132

    Sequential weak measurements allow for the direct extraction of individual density-matrix elements, rather than relying on global reconstruction of the entire density matrix, which opens a new avenue for the characterization of quantum systems. Nevertheless, extending the sequential scheme to multiqudit quantum systems is challenging due to the requirement of multiple coupling processes for each qudit and the lack of appropriate precision evaluation. To address these issues, we propose a resource-efficient scheme (RES) that directly characterizes the density matrix of general multiqudit systems while optimizing measurements and establishing a feasible estimation analysis. In the RES, an efficient observable of the quantum system is constructed such that a single meter state coupled to each qudit is sufficient to extract the corresponding density-matrix element. An appropriate model based on the statistical distribution of errors is utilized to evaluate the precision and feasibility of the scheme. We have experimentally applied the RES to the direct characterization of general single-photon qutrit states and two-photon entangled states. The results show that the RES outperforms sequential schemes in terms of efficiency and precision in both weak- and strong-coupling scenarios. This Letter sheds new light on the practical characterization of large-scale quantum systems and the investigation of their nonclassical properties.

  • Journal article
    Röser D, Padilla-Castillo JE, Ohayon B, Thomas R, Truppe S, Meijer G, Stellmer S, Wright SCet al., 2024,

    Hyperfine structure and isotope shifts of the (4s2) S0 1 →(4s4p) P1 1 transition in atomic zinc

    , Physical Review A, Vol: 109, ISSN: 2469-9926

    We report absolute frequency, isotope shift, radiative lifetime, and hyperfine structure measurements of the (4s2)S01→(4s4p)P11 (213.8 nm) transition in Zn I using a cryogenic buffer gas beam. Laser-induced fluorescence is collected with two orthogonally oriented detectors to take advantage of differences in the emission pattern of the isotopes. This enables a clear distinction between isotopes whose resonances are otherwise unresolved, and a measurement of the Zn67 hyperfine structure parameters, A(Zn67)=20(2)MHz and B(Zn67)=10(5)MHz. We reference our frequency measurements to an ultralow expansion cavity and achieve an uncertainty at the level of 1 MHz, about 1 percent of the natural linewidth of the transition.

  • Journal article
    Garratt D, Matthews M, Marangos J, 2024,

    Towards ultrafast soft X-ray spectroscopy of organic photovoltaic devices

    , Structural Dynamics, Vol: 11, ISSN: 2329-7778

    Novel ultrafast x-ray sources based on high harmonic generation and at x-ray free electron lasers are opening up new opportunities to resolve complex ultrafast processes in condensed phase systems with exceptional temporal resolution and atomic site specificity. In this perspective, we present techniques for resolving charge localization, transfer, and separation processes in organic semiconductors and organic photovoltaic devices with time-resolved soft x-ray spectroscopy. We review recent results in ultrafast soft x-ray spectroscopy of these systems and discuss routes to overcome the technical challenges in performing time-resolved x-ray experiments on photosensitive materials with poor thermal conductivity and low pump intensity thresholds for nonlinear effects.

  • Journal article
    Guo Z, Driver T, Beauvarlet S, Cesar D, Duris J, Franz PL, Alexander O, Bohler D, Bostedt C, Averbukh V, Cheng X, DiMauro LF, Doumy G, Forbes R, Gessner O, Glownia JM, Isele E, Kamalov A, Larsen KA, Li S, Li X, Lin MF, McCracken GA, Obaid R, ONeal JT, Robles RR, Rolles D, Ruberti M, Rudenko A, Slaughter DS, Sudar NS, Thierstein E, Tuthill D, Ueda K, Wang E, Wang AL, Wang J, Weber T, Wolf TJA, Young L, Zhang Z, Bucksbaum PH, Marangos JP, Kling MF, Huang Z, Walter P, Inhester L, Berrah N, Cryan JP, Marinelli Aet al., 2024,

    Experimental demonstration of attosecond pump–probe spectroscopy with an X-ray free-electron laser

    , Nature Photonics, ISSN: 1749-4885

    Pump–probe experiments with subfemtosecond resolution are the key to understanding electronic dynamics in quantum systems. Here we demonstrate the generation and control of subfemtosecond pulse pairs from a two-colour X-ray free-electron laser. By measuring the delay between the two pulses with an angular streaking diagnostic, we characterize the group velocity of the X-ray free-electron laser and show control of the pulse delay down to 270 as. We confirm the application of this technique to a pump–probe measurement in core-ionized para-aminophenol. These results reveal the ability to perform pump–probe experiments with subfemtosecond resolution and atomic site specificity.

  • Journal article
    Maillette de Buy Wenniger I, Thomas SE, Maffei M, Wein SC, Pont M, Belabas N, Prasad S, Harouri A, Lemaître A, Sagnes I, Somaschi N, Auffèves A, Senellart Pet al., 2023,

    Experimental Analysis of Energy Transfers between a Quantum Emitter and Light Fields.

    , Phys Rev Lett, Vol: 131

    Energy can be transferred between two quantum systems in two forms: unitary energy-that can be used to drive another system-and correlation energy-that reflects past correlations. We propose and implement experimental protocols to access these energy transfers in interactions between a quantum emitter and light fields. Upon spontaneous emission, we measure the unitary energy transfer from the emitter to the light field and show that it never exceeds half the total energy transfer and is reduced when introducing decoherence. We then study the interference of the emitted field and a coherent laser field at a beam splitter and show that the nature of the energy transfer quantitatively depends on the quantum purity of the emitted field.

  • Journal article
    Frasinski LJ, 2023,

    Correction: Cumulant mapping as the basis of multi-dimensional spectrometry.

    , Phys Chem Chem Phys, Vol: 25

    Correction for 'Cumulant mapping as the basis of multi-dimensional spectrometry' by Leszek J. Frasinski, Phys. Chem. Chem. Phys., 2022, 24, 20776-20787,

  • Journal article
    Wiesinger M, Stuhlmann F, Bohman M, Micke P, Will C, Yildiz H, Abbass F, Arndt BP, Devlin JA, Erlewein S, Fleck M, Jäger JI, Latacz BM, Schweitzer D, Umbrazunas G, Wursten E, Blaum K, Matsuda Y, Mooser A, Quint W, Soter A, Walz J, Smorra C, Ulmer Set al., 2023,

    Trap-integrated fluorescence detection with silicon photomultipliers for sympathetic laser cooling in a cryogenic Penning trap.

    , Rev Sci Instrum, Vol: 94

    We present a fluorescence-detection system for laser-cooled 9Be+ ions based on silicon photomultipliers (SiPMs) operated at 4 K and integrated into our cryogenic 1.9 T multi-Penning-trap system. Our approach enables fluorescence detection in a hermetically sealed cryogenic Penning-trap chamber with limited optical access, where state-of-the-art detection using a telescope and photomultipliers at room temperature would be extremely difficult. We characterize the properties of the SiPM in a cryocooler at 4 K, where we measure a dark count rate below 1 s-1 and a detection efficiency of 2.5(3)%. We further discuss the design of our cryogenic fluorescence-detection trap and analyze the performance of our detection system by fluorescence spectroscopy of 9Be+ ion clouds during several runs of our sympathetic laser-cooling experiment.

  • Journal article
    Ho C, Wright S, Sauer B, Tarbutt Met al., 2023,

    Systematic errors arising from polarization imperfections in measurements of the electron’s electric dipole moment

    , Physical Review Research, Vol: 5, ISSN: 2643-1564

    The electron’s electric dipole moment (eEDM) can be determined by polarizing the spin of an atom or a molecule and then measuring the spin precession frequency in an applied electric field. Radiation is used to polarize the spin and then analyze the precession angle, and the measurement is often sensitive to the polarization of this radiation. We show how systematic errors can arise when both the polarization of the radiation and the magnitude of the electric field are imperfectly controlled. We derive approximate analytical expressions for these errors, confirm their accuracy numerically, and show how they can be corrected empirically. We consider spin manipulation using single-photon pulses, Raman pulses, and Stimulated Raman Adiabatic Passage (STIRAP), and show that STIRAP provides better immunity to these systematic errors. An experimental study of these errors partly supports our findings but also reveals another potential error that is not captured by this analysis.

  • Journal article
    Ahyoune S, Álvarez Melcón A, Arguedas Cuendis S, Calatroni S, Cogollos C, Devlin J, DíazMorcillo A, DíezIbáñez D, Döbrich B, Galindo J, Gallego JD, GarcíaBarceló JM, Gimeno B, Golm J, Gu Y, Herwig L, Garcia Irastorza I, LozanoGuerrero AJ, Malbrunot C, MiraldaEscudé J, MonzóCabrera J, Navarro P, NavarroMadrid JR, Redondo J, ReinaValero J, Schmieden K, Schneemann T, Siodlaczek M, Ulmer S, Wuensch Wet al., 2023,

    A proposal for a low-frequency axion search in the 1–2 μ eV range and below with the babyIAXO magnet

    , Annalen der Physik, Vol: 535, ISSN: 0003-3804

    In the near future BabyIAXO will be the most powerful axion helioscope,relying on a custom-made magnet of two bores of 70 cm diameter and 10 mlong, with a total available magnetic volume of more than 7 m3. In thisdocument, it proposes and describe the implementation of low-frequencyaxion haloscope setups suitable for operation inside the BabyIAXO magnet.The RADES proposal has a potential sensitivity to the axion-photon couplingga𝜸 down to values corresponding to the KSVZ model, in the (currentlyunexplored) mass range between 1 and 2 𝛍 eV, after a total effective exposureof 440 days. This mass range is covered by the use of four differentlydimensioned 5-meter-long cavities, equipped with a tuning mechanism basedon inner turning plates. A setup like the one proposed will also allow anexploration of the same mass range for hidden photons coupled to photons.An additional complementary apparatus is proposed using LC circuits andexploring the low energy range (≈ 10−4 − 10−1 𝛍 eV). The setup includes acryostat and cooling system to cool down the BabyIAXO bore down to about 5K, as well as an appropriate low-noise signal amplification anddetection chain.

  • Journal article
    Rudolph T, Virmani SS, 2023,

    The two-qubit singlet/triplet measurement is universal for quantum computing given only maximally-mixed initial states

    , Nature Communications, Vol: 14, ISSN: 2041-1723

    In order to delineate which minimalistic physical primitives can enable the full power of universal quantum computing, it has been fruitful to consider various measurement based architectures which reduce or eliminate the use of coherent unitary evolution, and also involve operations that are physically natural. In this context previous works had shown that the triplet-singlet measurement of two qubit angular momentum (or equivalently two qubit exchange symmetry) yields the power of quantum computation given access to a few additional different single qubit states or gates. However, Freedman, Hastings and Shokrian-Zini1 recently proposed a remarkable conjecture, called the ‘STP=BQP’ conjecture, which states that the two-qubit singlet/triplet measurement is quantum computationally universal given only an initial ensemble of maximally mixed single qubits. In this work we prove this conjecture. This provides a method for quantum computing that is fully rotationally symmetric (i.e. reference frame independent), using primitives that are physically very-accessible, naturally resilient to certain forms of error, and provably the simplest possible.

  • Journal article
    Hutchison CDM, Baxter JM, Fitzpatrick A, Dorlhiac G, Fadini A, Perrett S, Maghlaoui K, Lefevre SB, Cordon-Preciado V, Ferreira JL, Chukhutsina VU, Garratt D, Barnard J, Galinis G, Glencross F, Morgan RM, Stockton S, Taylor B, Yuan L, Romei MG, Lin C-Y, Marangos JP, Schmidt M, Chatrchyan V, Buckup T, Morozov D, Park J, Park S, Eom I, Kim M, Jang D, Choi H, Hyun H, Park G, Nango E, Tanaka R, Owada S, Tono K, DePonte DP, Carbajo S, Seaberg M, Aquila A, Boutet S, Barty A, Iwata S, Boxer SG, Groenhof G, van Thor JJet al., 2023,

    Optical control of ultrafast structural dynamics in a fluorescent protein

    , NATURE CHEMISTRY, ISSN: 1755-4330
  • Journal article
    Smorra C, Abbass F, Schweitzer D, Bohman M, Devine JD, Dutheil Y, Hobl A, Arndt B, Bauer BB, Devlin JA, Erlewein S, Fleck M, Jäger JI, Latacz BM, Micke P, Schiffelholz M, Umbrazunas G, Wiesinger M, Will C, Wursten E, Yildiz H, Blaum K, Matsuda Y, Mooser A, Ospelkaus C, Quint W, Soter A, Walz J, Yamazaki Y, Ulmer Set al., 2023,

    BASE-STEP: a transportable antiproton reservoir for fundamental interaction studies

    , Review of Scientific Instruments, Vol: 94, ISSN: 0034-6748

    Currently, the world's only source of low-energy antiprotons is the AD/ELENA facility located at CERN. To date, all precision measurements on single antiprotons have been conducted at this facility and provide stringent tests of fundamental interactions and their symmetries. However, magnetic field fluctuations from the facility operation limit the precision of upcoming measurements. To overcome this limitation, we have designed the transportable antiproton trap system BASE-STEP to relocate antiprotons to laboratories with a calm magnetic environment. We anticipate that the transportable antiproton trap will facilitate enhanced tests of charge, parity, and time-reversal invariance with antiprotons and provide new experimental possibilities of using transported antiprotons and other accelerator-produced exotic ions. We present here the technical design of the transportable trap system. This includes the transportable superconducting magnet, the cryogenic inlay consisting of the trap stack and detection systems, and the differential pumping section to suppress the residual gas flow into the cryogenic trap chamber.

  • Journal article
    Yu S, Zhong Z-P, Fang Y, Patel RB, Li Q-P, Liu W, Li Z, Xu L, Sagona-Stophel S, Mer E, Thomas SE, Meng Y, Li Z-P, Yang Y-Z, Wang Z-A, Guo N-J, Zhang W-H, Tranmer GK, Dong Y, Wang Y-T, Tang J-S, Li C-F, Walmsley IA, Guo G-Cet al., 2023,

    A universal programmable Gaussian boson sampler for drug discovery

  • Journal article
    Alexander O, Barnard J, Larsen E, Avni T, Jarosch S, Ferchaud C, Gregory A, Parker S, Galinis G, Tofful A, Garratt D, Matthews M, Marangos Jet al., 2023,

    Observation of recollision-based high-harmonic generation in liquid isopropanol and the role of electron scattering

    , Physical Review Research, ISSN: 2643-1564
  • Journal article
    Latacz BM, Arndt BP, Devlin JA, Erlewein SR, Fleck M, Jäger JI, Micke P, Umbrazunas G, Wursten E, Abbass F, Schweitzer D, Wiesinger M, Will C, Yildiz H, Blaum K, Matsuda Y, Mooser A, Ospelkaus C, Smorra C, Sótér A, Quint W, Walz J, Yamazaki Y, Ulmer Set al., 2023,

    Ultra-thin polymer foil cryogenic window for antiproton deceleration and storage.

    , Rev Sci Instrum, Vol: 94

    We present the design and characterization of a cryogenic window based on an ultra-thin aluminized biaxially oriented polyethylene terephthalate foil at T < 10 K, which can withstand a pressure difference larger than 1 bar at a leak rate <1×10-9 mbar l/s. Its thickness of ∼1.7 μm makes it transparent to various types of particles over a broad energy range. To optimize the transfer of 100 keV antiprotons through the window, we tested the degrading properties of different aluminum coated polymer foils of thicknesses between 900 and 2160 nm, concluding that 1760 nm foil decelerates antiprotons to an average energy of 5 keV. We have also explicitly studied the permeation as a function of coating thickness and temperature and have performed extensive thermal and mechanical endurance and stress tests. Our final design integrated into the experiment has an effective open surface consisting of seven holes with a diameter of 1 mm and will transmit up to 2.5% of the injected 100 keV antiproton beam delivered by the Antiproton Decelerator and Extra Low ENergy Antiproton ring facility of CERN.

  • Journal article
    Smith AWR, Paige AJ, Kim MS, 2023,

    Faster variational quantum algorithms with quantum kernel-based surrogate models

    , Quantum Science and Technology, Vol: 8, ISSN: 2058-9565

    We present a new optimization strategy for small-to-intermediate scale variational quantum algorithms (VQAs) on noisy near-term quantum processors which uses a Gaussian process surrogate model equipped with a classically-evaluated quantum kernel. VQAs are typically optimized using gradient-based approaches however these are difficult to implement on current noisy devices, requiring large numbers of objective function evaluations. Our approach shifts this computational burden onto the classical optimizer component of these hybrid algorithms, greatly reducing the number of quantum circuit evaluations required from the quantum processor. We focus on the variational quantum eigensolver (VQE) algorithm and demonstrate numerically that these surrogate models are particularly well suited to the algorithm's objective function. Next, we apply these models to both noiseless and noisy VQE simulations and show that they exhibit better performance than widely-used classical kernels in terms of final accuracy and convergence speed. Compared to the typically-used stochastic gradient-descent approach to VQAs, our quantum kernel-based approach is found to consistently achieve significantly higher accuracy while requiring less than an order of magnitude fewer quantum circuit executions. We analyze the performance of the quantum kernel-based models in terms of the kernels' induced feature spaces and explicitly construct their feature maps. Finally, we describe a scheme for approximating the best-performing quantum kernel using a classically-efficient tensor network representation of its input state and so provide a pathway for scaling this strategy to larger systems.

  • Journal article
    Yu S, Zhong Z-P, Fang Y, Patel RB, Li Q-P, Liu W, Li Z, Xu L, Sagona-Stophel S, Mer E, Thomas SE, Meng Y, Li Z-P, Yang Y-Z, Wang Z-A, Guo N-J, Zhang W-H, Tranmer GK, Dong Y, Wang Y-T, Tang J-S, Li C-F, Walmsley IA, Guo G-Cet al., 2023,

    A universal programmable Gaussian boson sampler for drug discovery.

    , Nat Comput Sci, Vol: 3, Pages: 839-848

    Gaussian boson sampling (GBS) has the potential to solve complex graph problems, such as clique finding, which is relevant to drug discovery tasks. However, realizing the full benefits of quantum enhancements requires large-scale quantum hardware with universal programmability. Here we have developed a time-bin-encoded GBS photonic quantum processor that is universal, programmable and software-scalable. Our processor features freely adjustable squeezing parameters and can implement arbitrary unitary operations with a programmable interferometer. Leveraging our processor, we successfully executed clique finding on a 32-node graph, achieving approximately twice the success probability compared to classical sampling. As proof of concept, we implemented a versatile quantum drug discovery platform using this GBS processor, enabling molecular docking and RNA-folding prediction tasks. Our work achieves GBS circuitry with its universal and programmable architecture, advancing GBS toward use in real-world applications.

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