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Journal articleSchofield RC, Fu M, Clarke E, et al., 2024,
Bose–Einstein condensation of light in a semiconductor quantum well microcavity
, Nature Photonics, ISSN: 1749-4885When particles with integer spin accumulate at low temperature and high density, they undergo Bose–Einstein condensation (BEC). Atoms, magnons, solid-state excitons, surface plasmon polaritons and excitons coupled to light exhibit BEC, which results in high coherence due to massive occupation of the respective system’s ground state. Surprisingly, photons were shown to exhibit BEC recently in organic-dye-flled optical microcavities, which—owing to the photon’s low mass—occurs at room temperature. Here we demonstrate that photons within an inorganic semiconductor microcavity also thermalize and undergo BEC. Although semiconductor lasers are understood to operate out of thermal equilibrium, we identify a region of good thermalization in our system where we can clearly distinguish laser action from BEC. Semiconductor microcavities are a robust system for exploring the physics and applications of quantum statistical photon condensates. In practical terms, photon BECs ofer their critical behaviour at lower thresholds than lasers. Our study shows two further advantages: the lack of dark electronic states in inorganic semiconductors allows these BECs to be sustained continuously; and quantum wells ofer stronger photon–photon scattering. We measure an unoptimized interaction parameter ( g̃ ≳ 10–3), which is large enough to access the rich physics of interactions within BECs, such as superfuid light.
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Journal articleLatacz BM, Fleck M, Jäger JI, et al., 2024,
Orders of Magnitude Improved Cyclotron-Mode Cooling for Nondestructive Spin Quantum Transition Spectroscopy with Single Trapped Antiprotons.
, Phys Rev Lett, Vol: 133We demonstrate efficient subthermal cooling of the modified cyclotron mode of a single trapped antiproton and reach particle temperatures T_{+}=E_{+}/k_{B} below 200 mK in preparation times shorter than 500 s. This corresponds to the fastest resistive single-particle cyclotron cooling to subthermal temperatures ever demonstrated. By cooling trapped particles to such low energies, we demonstrate the detection of antiproton spin transitions with an error rate <0.000 023, more than 3 orders of magnitude better than in previous best experiments. This method has enormous impact on multi-Penning-trap experiments that measure magnetic moments with single nuclear spins for tests of matter and antimatter symmetry, high-precision mass spectrometry, and measurements of electron g factors bound to highly charged ions that test quantum electrodynamics and establish standards for magnetometry.
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Journal articleTofful A, Baynham CFA, Curtis EA, et al., 2024,
<SUP>171</SUP>Yb<SUP>+</SUP> optical clock with 2.2 x 10<SUP>-18</SUP> systematic uncertainty and absolute frequency measurements
, METROLOGIA, Vol: 61, ISSN: 0026-1394 -
Journal articleDriver T, Mountney M, Wang J, et al., 2024,
Attosecond delays in X-ray molecular ionization.
, Nature, Vol: 632, Pages: 762-767The photoelectric effect is not truly instantaneous but exhibits attosecond delays that can reveal complex molecular dynamics1-7. Sub-femtosecond-duration light pulses provide the requisite tools to resolve the dynamics of photoionization8-12. Accordingly, the past decade has produced a large volume of work on photoionization delays following single-photon absorption of an extreme ultraviolet photon. However, the measurement of time-resolved core-level photoionization remained out of reach. The required X-ray photon energies needed for core-level photoionization were not available with attosecond tabletop sources. Here we report measurements of the X-ray photoemission delay of core-level electrons, with unexpectedly large delays, ranging up to 700 as in NO near the oxygen K-shell threshold. These measurements exploit attosecond soft X-ray pulses from a free-electron laser to scan across the entire region near the K-shell threshold. Furthermore, we find that the delay spectrum is richly modulated, suggesting several contributions, including transient trapping of the photoelectron owing to shape resonances, collisions with the Auger-Meitner electron that is emitted in the rapid non-radiative relaxation of the molecule and multi-electron scattering effects. The results demonstrate how X-ray attosecond experiments, supported by comprehensive theoretical modelling, can unravel the complex correlated dynamics of core-level photoionization.
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Journal articleXiao X, Yang JJ, Millard TS, et al., 2024,
Nanofocusing in critically coupled nanogap waveguide resonators
, ACS Photonics, Vol: 11, Pages: 2836-2842, ISSN: 2330-4022Coupling between optical antenna resonances is a powerful way to control the distribution of light in nanoscale systems. When the strength of coupling is fine-tuned against resonance loss, a critical coupling condition is often met, where energy can be efficiently directed between the system’s components. In this work, we use this concept to nanofocus optical energy into the 50 nm gap of a waveguide resonator, which on its own cannot be excited by external illumination. Light couples to the waveguide antenna via Fano interference with a bar antenna dimer. As a composite antenna, the shifting of the dimer relative to the waveguide resonator enables the precise tuning of their mutual coupling. We find a critical coupling condition where light is maximally focused into the waveguide’s gap corresponding to unity coupling cooperativity. Our interpretation of critical-coupling-induced nanofocusing is supported by the simultaneous maximization of both second and third harmonic generation at the critical condition.
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Journal articleWill C, Wiesinger M, Micke P, et al., 2024,
Image-Current Mediated Sympathetic Laser Cooling of a Single Proton in a Penning Trap Down to 170 mK Axial Temperature.
, Phys Rev Lett, Vol: 133We demonstrate a new temperature record for image-current mediated sympathetic cooling of a single proton in a cryogenic Penning trap by laser-cooled ^{9}Be^{+}. An axial mode temperature of 170 mK is reached, which is a 15-fold improvement compared to the previous best value. Our cooling technique is applicable to any charged particle, so that the measurements presented here constitute a milestone toward the next generation of high-precision Penning-trap measurements with exotic particles.
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Journal articleJae J, Lee J, Kim MS, et al., 2024,
Contextual quantum metrology
, npj Quantum Information, Vol: 10, ISSN: 2056-6387We demonstrate that the contextuality of measurement selection can enhance the precision of quantum metrology with a simple linear optical experiment. Contextuality is a nonclassical property known as a resource for various quantum information processing tasks. Recent studies show that contextuality by anomalous weak values can be utilized to enhance metrological precision, unraveling the role of contextuality in quantum metrology. Our contextual quantum metrology (coQM) scheme can elevate the precision of the optical polarimetry as much as 6 times the precision limit given by the Quantum Fisher Information. We achieve the contextuality-enabled enhancement with two mutually complementary measurements, whereas, in the conventional method, some optimal measurements to achieve the precision limit are either theoretically challenging to find or experimentally infeasible to realize. These results highlight that the contextuality of measurement selection is applicable in practice for quantum metrology.
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Journal articleAthanasakis-Kaklamanakis M, Wilkins SG, Lassègues P, et al., 2024,
Radiative lifetime of the A Π1/2 2 state in RaF with relevance to laser cooling
, Physical Review A, Vol: 110, ISSN: 2469-9926The radiative lifetime of the AΠ1/22 (v=0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate Γ=2.86(8)×107 s-1 are of relevance to the laser cooling of RaF via the optically closed AΠ1/22←Xς1/22 transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Owing to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just three cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8P3/2 state in Fr to be 83(3) ns, in agreement with literature.
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Journal articleMichniewicz J, Kim MS, 2024,
Leveraging off-the-shelf silicon chips for quantum computing
, Applied Physics Letters, Vol: 124, ISSN: 0003-6951There is a growing demand for quantum computing across various sectors, including finance, materials, and studying chemical reactions. A promising implementation involves semiconductor qubits utilizing quantum dots within transistors. While academic research labs currently produce their own devices, scaling this process is challenging, requires expertise, and results in devices of varying quality. Some initiatives are exploring the use of commercial transistors, offering scalability, improved quality, affordability, and accessibility for researchers. This paper delves into potential realizations and the feasibility of employing off-the-shelf commercial devices for qubits. It addresses challenges such as noise, coherence, limited customizability in large industrial fabs, and scalability issues. The exploration includes discussions on potential manufacturing approaches for early versions of small qubit chips. The use of state-of-the-art transistors as hosts for quantum dots, incorporating readout techniques based on charge sensing or reflectometry, and methods like electron shuttling for qubit connectivity are examined. Additionally, more advanced designs, including 2D arrays and crossbar or DRAM-like access arrays, are considered for the path toward accessible quantum computing.
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Journal articleHaug T, Lee S, Kim MS, 2024,
Efficient quantum algorithms for stabilizer entropies
, Physical Review Letters, Vol: 132, ISSN: 0031-9007Stabilizer entropies (SEs) are measures of nonstabilizerness or “magic” that quantify the degree to whicha state is described by stabilizers. SEs are especially interesting due to their connections to scrambling,localization and property testing. However, applications have been limited so far as previously knownmeasurement protocols for SEs scale exponentially with the number of qubits. Here, we efficiently measureSEs for integer R´enyi index n > 1 via Bell measurements. The SE of N-qubit quantum states can bemeasured with OðnÞ copies and OðnNÞ classical computational time, where for even n we additionallyrequire the complex conjugate of the state. We provide efficient bounds of various nonstabilizernessmonotones that are intractable to compute beyond a few qubits. Using the IonQ quantum computer, wemeasure SEs of random Clifford circuits doped with non-Clifford gates and give bounds for the stabilizerfidelity, stabilizer extent, and robustness of magic. We provide efficient algorithms to measure Clifford averaged 4n-point out-of-time-order correlators and multifractal flatness. With these measures we study thescrambling time of doped Clifford circuits and random Hamiltonian evolution depending on nonstabilizer ness. Counterintuitively, random Hamiltonian evolution becomes less scrambled at long times, which wereveal with the multifractal flatness. Our results open up the exploration of nonstabilizerness with quantumcomputers.
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Journal articleZhu R, Pike-Burke C, Mintert F, 2024,
Active learning for quantum mechanical measurements
, Physical Review A, Vol: 109, ISSN: 2469-9926The experimental evaluation of many quantum mechanical quantities requires the estimation of several directly measurable observables, such as local observables. Due to the necessity to repeat experiments on individual quantum systems in order to estimate expectation values of observables, the question of how many repetitions to allocate to a given directly measurable observable arises. We show that an active learning scheme can help to improve such allocations, and the resultant decrease in experimental repetitions required to evaluate a quantity with the desired accuracy increases with the size of the underlying quantum mechanical system.
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Journal articleMok W-K, Zhang H, Haug T, et al., 2024,
Rigorous noise reduction with quantum autoencoders
, AVS QUANTUM SCIENCE, Vol: 6 -
Journal articlePopa S, Schaller S, Fielicke A, et al., 2024,
Understanding Inner-Shell Excitations in Molecules through Spectroscopy of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" 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="http://www.w3.org/1998/Math/MathML" 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="http://www.w3.org/1998/Math/MathML" 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="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msup>&l
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Journal articleWalraven EF, Tarbutt MR, Karman T, 2024,
Scheme for deterministic loading of laser-cooled molecules into optical tweezers
, Physical Review Letters, Vol: 132, ISSN: 0031-9007We 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.
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Journal articleCornish SL, Tarbutt MR, Hazzard KRA, 2024,
Quantum computation and quantum simulation with ultracold molecules
, NATURE PHYSICS, Vol: 20, Pages: 730-740, ISSN: 1745-2473 -
Journal articleShi B, Mintert F, 2024,
Quantum simulations of time-dependent Hamiltonians beyond the quasistatic approximation
, Physical Review Research, Vol: 6, ISSN: 2643-1564Existing approaches to analogue quantum simulations of time-dependent quantum systems relyon perturbative corrections to quantum simulations of time-independent quantum systems. Weovercome this restriction to perturbative treatments with an approach based on flow equations anda multi-mode Fourier expansion. The potential of the quantum simulations that can be achievedwith our approach is demonstrated with the pedagogical example of a Lambda-system and thequench in finite time through a quantum phase transition of a Chern insulator in a driven noninteracting Hubbard system. The example of the Lambda-system demonstrates the ability of ourapproach to describe situations beyond the validity of adiabatic approximations.
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Journal articleTang Y, Dhar HS, Oulton RF, et al., 2024,
Breakdown of Temporal Coherence in Photon Condensates.
, Phys Rev Lett, Vol: 132The temporal coherence of an ideal Bose gas increases as the system approaches the Bose-Einstein condensation threshold from below, with coherence time diverging at the critical point. However, counterexamples have been observed for condensates of photons formed in an externally pumped, dye-filled microcavity, wherein the coherence time decreases rapidly for increasing particle number above threshold. This Letter establishes intermode correlations as the central explanation for the experimentally observed dramatic decrease in the coherence time beyond critical pump power.
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Journal articleAlexander O, Egun F, Rego L, et al., 2024,
Attosecond impulsive stimulated x-ray Raman scattering in liquid water
, Science Advances, ISSN: 2375-2548Here, we report the measurement of impulsive stimulated x-ray Raman scattering in neutral liquid water. An attosecond pulse drives the excitations of an electronic wavepacket in water molecules. The process comprises two steps: a transition to core-excited states near the oxygen atoms accompanied by transition to a valence-excited states. Thus, the wavepacket is impulsivelycreated at a specific atomic site within a few hundred attoseconds through a non-linear interaction between the water and the x-ray pulse. We observe this nonlinear signature in an intensity dependent Stokes Raman sideband at 526 eV. Our measurements are supported by our state-of-the-art calculations based on the polarisation response of water dimers in bulk solvation and propagation of attosecond x-ray pulses at liquid density.
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Journal articleGuo Z, Driver T, Beauvarlet S, et al., 2024,
Experimental demonstration of attosecond pump-probe spectroscopy with an X-ray free-electron laser
, NATURE PHOTONICS, ISSN: 1749-4885 -
Journal articlePopa S, Schaller S, Fielicke A, et al., 2024,
Understanding inner-shell excitations in molecules through spectroscopy of the 4f hole states of YbF
, Physical Review X, Vol: 14, ISSN: 2160-3308Molecules 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.
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Journal articleCheng C, Frasinski LJ, Allum F, et al., 2024,
Multiparticle cumulant mapping for Coulomb explosion imaging: Calculations and algorithm
, PHYSICAL REVIEW A, Vol: 109, ISSN: 2469-9926 -
Journal articleThomas SE, Wagner L, Joos R, et 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: 2375-2548A 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.
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Journal articleTang Y, Dhar HS, Oulton RF, et al., 2024,
Photon-photon correlation of condensed light in a microcavity
, Physical Review A (atomic, molecular, and optical physics and quantum information), Vol: 109, ISSN: 2469-9926The study of temporal coherence in a Bose-Einstein condensate of photons can be challenging, especially in the presence of correlations between the photonic modes. In this work, we use a microscopic, multimode model of photonic condensation inside a dye-filled microcavity and the quantum regression theorem to derive an analytical expression for the equation of motion of the photon-photon correlation function. This allows us to derive the coherence time of the photonic modes and identify a nonmonotonic dependence of the temporal coherence of the condensed light with the cutoff frequency of the microcavity.
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Journal articleAlaa El-Din K, Alexander O, Frasinski L, et al., 2024,
Efficient prediction of attosecond two-colour pulses from an X-ray free-electron laser with machine learning
, Scientific Reports, Vol: 14, ISSN: 2045-2322X-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.
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Journal articleGreenaway S, Petiziol F, Zhao H, et al., 2024,
Variational quantum gate optimization at the pulse level
, SciPost Physics, Vol: 16, ISSN: 2542-4653We experimentally investigate the viability of a variational quantum gate optimizationprotocol informed by the underlying physical Hamiltonian of fixed-frequency transmonqubits. Through the successful experimental optimization of two and three qubit quan-tum gates the utility of the scheme for obtaining gates based on static effective Hamilto-nians is demonstrated. The limits of such a strategy are investigated through the opti-mization of a time-dependent, Floquet-engineered gate, however parameter drift is iden-tified as a key limiting factor preventing the implementation of such a scheme which thevariational optimization protocol is unable to overcome.
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Journal articleYu S, Liu W, Tao S-J, et al., 2024,
A von-Neumann-like photonic processor and its application in studying quantum signature of chaos
, LIGHT-SCIENCE & APPLICATIONS, Vol: 13, ISSN: 2095-5545 -
Journal articleWang Z, Wang F, Vovrosh J, et al., 2024,
Quantum simulation of hadronic states with Rydberg-dressed atoms
, PHYSICAL REVIEW A, Vol: 109, ISSN: 2469-9926 -
Journal articleTang H, Shang X-W, Shi Z-Y, et al., 2024,
Simulating photosynthetic energy transport on a photonic network
, npj Quantum Information, Vol: 10, ISSN: 2056-6387Quantum 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.
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Journal articleStray B, Ennis O, Hedges S, et 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: 2639-0213This 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.
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Journal articleGreenaway S, Smith A, Mintert F, et al., 2024,
Analogue Quantum Simulation with Fixed-Frequency Transmon Qubits
, QUANTUM, Vol: 8, ISSN: 2521-327X
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