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Journal articleHofsäss S, Padilla-Castillo JE, Wright SC, et al., 2023,
High-resolution isotope-shift spectroscopy of Cd i
, Physical Review Research, Vol: 5, ISSN: 2643-1564We present absolute frequency measurements of the 1P1←1S0 (229-nm) and 3P1←1S0 (326-nm) transitions for all naturally occurring isotopes of cadmium. The isotope shifts and hyperfine intervals of the fermionic isotopes are determined with an accuracy of 3.3 MHz. We find that quantum interference in the laser-induced fluorescence spectra of the 1P1←1S0 transition causes a variation of up to 29(5) MHz in determining the hyperfine splitting when not accounted for with an appropriate model. Using a King-plot analysis, we extract the field- and mass-shift parameters and determine nuclear charge radius differences for the fermions. The lifetime of the 1P1 state is determined to be 1.60(5) ns by measuring the natural linewidth of the 1P1←1S0 transition. These results resolve significant discrepancies among previous measurements.
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Journal articleAlexander OG, Marangos JP, Ruberti M, et al., 2023,
Attosecond electron dynamics in molecular systems
, Advances in Atomic Molecular and Optical Physics, Vol: 72, Pages: 183-251, ISSN: 1049-250XIn this paper we review the topic of attosecond electron dynamics in molecular systems. We present a digest of recent research on this topic conducted by ourselves and other researchers with the intention of providing an accessible, but rigorous, account of the current state of this intriguing field of research. A short account of the background quantum theory is given before discussing recent theoretical advances on understanding correlation driven electron dynamics and electron nuclear coupling in molecules undergoing fast photoionization. We then review experimental advances, using both high harmonic generation and XFEL based ultrafast x-ray pulses, and provide three recent case studies from our own work to illustrate this. The final sections look forward to the next steps in this field: we discuss the prospect for controlling attochemistry as well as extending attosecond measurement methods to electron dynamics in larger molecules and condensed phase systems.
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Journal articleHanks M, Kim MS, 2022,
Fault tolerance in qudit circuit design
, PHYSICAL REVIEW A, Vol: 106, ISSN: 2469-9926 -
Journal articleFasoulakis A, Major KDD, Hoggarth RAA, et al., 2022,
Uniaxial strain tuning of organic molecule single photon sources
, NANOSCALE, Vol: 15, Pages: 177-184, ISSN: 2040-3364 -
Journal articleRaii O, Mintert F, Burgarth D, 2022,
Scalable quantum control and non-Abelian anyon creation in the Kitaev honeycomb model
, PHYSICAL REVIEW A, Vol: 106, ISSN: 2469-9926 -
Journal articleOhayon B, Hofsäss S, Padilla-Castillo JE, et al., 2022,
Isotope shifts in cadmium as a sensitive probe for physics beyond the standard model
, New Journal of Physics, Vol: 24, ISSN: 1367-2630Isotope shifts (ISs) of atomic energy levels are sensitive probes of nuclear structure and new physics beyond the standard model. We present an analysis of the ISs of the cadmium atom (Cd I) and singly charged cadmium ion (Cd II). ISs of the 229 nm, 326 nm, 361 nm and 480 nm lines of Cd I are measured with a variety of techniques; buffer-gas-cooled beam spectroscopy, capturing atoms in a magneto-optic-trap, and optical pumping. IS constants for the D1 and D2 lines of Cd II are calculated with high accuracy by employing analytical response relativistic coupled-cluster theory in the singles, doubles and triples approximations. Combining the calculations for Cd II with experiments, we infer IS constants for all low-lying transitions in Cd I. We benchmark existing calculations via different many-body methods against these constants. Our calculations for Cd II enable nuclear charge radii of Cd isotopes to be extracted with unprecedented accuracy. The combination of our precise calculations and measurements shows that King plots for Cd I can improve the state-of-the-art sensitivity to a new heavy boson by up to two orders of magnitude.
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Journal articleAlonso I, Alpigiani C, Altschul B, et al., 2022,
Cold atoms in space: community workshop summary and proposed road-map
, EPJ QUANTUM TECHNOLOGY, Vol: 9, ISSN: 2662-4400- Author Web Link
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- Citations: 10
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Journal articleHaug T, Kim MS, 2022,
Natural parametrized quantum circuit
, PHYSICAL REVIEW A, Vol: 106, ISSN: 2469-9926- Author Web Link
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- Citations: 4
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Journal articleBarnard J, Lee J, Alexander O, et al., 2022,
Delivery of stable ultra-thin liquid sheets in vacuum for biochemical spectroscopy
, Frontiers in Molecular Biosciences, Vol: 9, ISSN: 2296-889XThe development of ultra-thin flat liquid sheets capable of running in vacuum has provided an exciting new target for X-ray absorption spectroscopy in the liquid and solution phases. Several methods have become available for delivering in-vacuum sheet jets using different nozzle designs. We compare the sheets produced by two different types of nozzle; a commercially available borosillicate glass chip using microfluidic channels to deliver colliding jets, and an in-house fabricated fan spray nozzle which compresses the liquid on an axis out of a slit to achieve collision conditions. We find in our tests that both nozzles are suitable for use in X-ray absorption spectroscopy with the fan spray nozzle producing thicker but more stable jets than the commercial nozzle. We also provide practical details of how to run these nozzles in vacuum.
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Journal articleSchwickert D, Ruberti M, Kolorenc P, et al., 2022,
Charge-induced chemical dynamics in glycine probed with time-resolved Auger electron spectroscopy
, STRUCTURAL DYNAMICS-US, Vol: 9- Author Web Link
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- Citations: 1
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Journal articleBellini M, Kwon H, Biagi N, et al., 2022,
Demonstrating quantum microscopic reversibility using coherent states of light
, Physical Review Letters, Vol: 129, Pages: 1-6, ISSN: 0031-9007The principle of microscopic reversibility lies at the core of fluctuation theorems, which have extended our understanding of the second law of thermodynamics to the statistical level. In the quantum regime, however, this elementary principle should be amended as the system energy cannot be sharply determined at a given quantum phase space point. In this Letter, we propose and experimentally test a quantum generalization of the microscopic reversibility when a quantum system interacts with a heat bath through energy-preserving unitary dynamics. Quantum effects can be identified by noting that the backward process is less likely to happen in the existence of quantum coherence between the system’s energy eigenstates. The experimental demonstration has been realized by mixing coherent and thermal states in a beam splitter, followed by heterodyne detection in an optical setup. We verify that the quantum modification for the principle of microscopic reversibility is critical in the low-temperature limit, while the quantum-to-classical transition is observed as the temperature of the thermal field gets higher.
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Journal articleTarrant J, Khokhlova M, Averbukh V, 2022,
Interferometry of quantum revivals (vol 157, 054304, 2022)
, JOURNAL OF CHEMICAL PHYSICS, Vol: 157, ISSN: 0021-9606 -
Journal articleKoukoulekidis N, Kwon H, Jee HH, et al., 2022,
Faster Born probability estimation via gate merging and frame optimisation
, Quantum, Vol: 6, Pages: 838-838, ISSN: 2521-327XOutcome probability estimation via classical methods is an important task for validating quantum computing devices. Outcome probabilities of any quantum circuit can be estimated using Monte Carlo sampling, where the amount of negativity present in the circuit frame representation quantifies the overhead on the number of samples required to achieve a certain precision. In this paper, we propose two classical sub-routines: circuit gate merging and frame optimisation, which optimise the circuit representation to reduce the sampling overhead. We show that the runtimes of both sub-routines scale polynomially in circuit size and gate depth. Our methods are applicable to general circuits, regardless of generating gate sets, qudit dimensions and the chosen frame representations for the circuit components. We numerically demonstrate that our methods provide improved scaling in the negativity overhead for all tested cases of random circuits with Clifford+T and Haar-random gates, and that the performance of our methods compares favourably with prior quasi-probability simulators as the number of non-Clifford gates increases.
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Journal articleKoukoulekidis N, Jee H, Jennings D, et al., 2022,
Faster Born probability estimation via gate merging and frame optimisation
, Quantum, Vol: 6, Pages: 838-838, ISSN: 2521-327XOutcome probability estimation via classical methods is an important task for validating quantum computing devices. Outcome probabilities of any quantum circuit can be estimated using Monte Carlo sampling, where the amount of negativity present in the circuit frame representation quantifies the overhead on the number of samples required to achieve a certain precision. In this paper, we propose two classical sub-routines: circuit gate merging and frame optimisation, which optimise the circuit representation to reduce the sampling overhead. We show that the runtimes of both sub-routines scale polynomially in circuit size and gate depth. Our methods are applicable to general circuits, regardless of generating gate sets, qudit dimensions and the chosen frame representations for the circuit components. We numerically demonstrate that our methods provide improved scaling in the negativity overhead for all tested cases of random circuits with Clifford+T and Haar-random gates, and that the performance of our methods compares favourably with prior quasi-probability simulators as the number of non-Clifford gates increases.
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Journal articleBressanini G, Kwon H, Kim MS, 2022,
Noise thresholds for classical simulability of nonlinear boson sampling
, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 106, Pages: 1-9, ISSN: 1050-2947Boson sampling, a computational problem conjectured to be hard to simulate on a classical machine, is a promising candidate for an experimental demonstration of quantum advantage using bosons. However, inevitable experimental noise and imperfections, such as loss in the interferometer and random counts at the detectors, could challenge the sampling task from entering the regime where quantum advantage is achievable. In this work we introduce higher-order nonlinearities as a means to enhance the computational complexity of the problem and the protocol's robustness against noise, i.e., to increase the noise threshold that allows us to perform an efficient classical simulation of the problem. Using a phase-space method based on the negativity volume of the relevant quasiprobability distributions, we establish a necessary nonclassicality condition that any experimental proof of quantum advantage must satisfy. Our results indicate that the addition of single-mode Kerr nonlinearity at the input-state preparation level, while retaining a linear-optical evolution, makes the boson-sampling protocol more robust against noise and consequently relaxes the constraints on the noise parameters required to show quantum advantage.
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Journal articleZhang H, Wan L, Haug T, et al., 2022,
Resource-efficient high-dimensional subspace teleportation with a quantum autoencoder.
, Science Advances, Vol: 8, Pages: 1-11, ISSN: 2375-2548Quantum autoencoders serve as efficient means for quantum data compression. Here, we propose and demonstrate their use to reduce resource costs for quantum teleportation of subspaces in high-dimensional systems. We use a quantum autoencoder in a compress-teleport-decompress manner and report the first demonstration with qutrits using an integrated photonic platform for future scalability. The key strategy is to compress the dimensionality of input states by erasing redundant information and recover the initial states after chip-to-chip teleportation. Unsupervised machine learning is applied to train the on-chip autoencoder, enabling the compression and teleportation of any state from a high-dimensional subspace. Unknown states are decompressed at a high fidelity (~0.971), obtaining a total teleportation fidelity of ~0.894. Subspace encodings hold great potential as they support enhanced noise robustness and increased coherence. Laying the groundwork for machine learning techniques in quantum systems, our scheme opens previously unidentified paths toward high-dimensional quantum computing and networking.
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Journal articleSong W, Lim Y, Jeong K, et al., 2022,
Polynomial T-depth quantum solvability of noisy binary linear problem: from quantum-sample preparation to main computation
, New Journal of Physics, Vol: 24, Pages: 1-11, ISSN: 1367-2630The noisy binary linear problem (NBLP) is known as a computationally hard problem, and therefore, it offers primitives for post-quantum cryptography. An efficient quantum NBLP algorithm that exhibits a polynomial quantum sample and time complexities has recently been proposed. However, the algorithm requires a large number of samples to be loaded in a highly entangled state and it is unclear whether such a precondition on the quantum speedup can be obtained efficiently. Here, we present a complete analysis of the quantum solvability of the NBLP by considering the entire algorithm process, namely from the preparation of the quantum sample to the main computation. By assuming that the algorithm runs on 'fault-tolerant' quantum circuitry, we introduce a reasonable measure of the computational time cost. The measure is defined in terms of the overall number of T gate layers, referred to as T-depth complexity. We show that the cost of solving the NBLP can be polynomial in the problem size, at the expense of an exponentially increasing logical qubits.
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Journal articleSempere Llagostera S, Patel RB, Walmsley IA, et al., 2022,
Experimentally finding dense subgraphs using a time-bin encoded Gaussian boson sampling device
, Physical Review X, Vol: 12, Pages: 1-12, ISSN: 2160-3308Gaussian boson sampling (GBS) is a quantum computing concept based on drawing samples from a multimode nonclassical Gaussian state using photon-number resolving detectors. It was initially posed as a near-term approach to achieve quantum advantage, and several applications have beenproposed since, including the calculation of graph features. For the first time, we use a time-bin encoded interferometer to implement GBS experimentally and extract samples to enhance the search for dense subgraphs in a graph. Our results indicate an improvement over classical methods for subgraphs of sizes three and four in a graph containing ten nodes. In addition, we numerically explore the role of imperfections in the optical circuit and on the performance of the algorithm.
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Journal articleLiu W, Ivady V, Li Z-P, et al., 2022,
Coherent dynamics of multi-spin V<sub>B</sub><SUP>-</SUP> center in hexagonal boron nitride
, NATURE COMMUNICATIONS, Vol: 13- Author Web Link
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- Citations: 20
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Journal articleZhang C, Tarbutt M, 2022,
Quantum computation in a hybrid array of molecules and Rydberg atoms
, PRX Quantum, Vol: 3, Pages: 1-17, ISSN: 2691-3399We show that an array of polar molecules interacting with Rydberg atoms is a promising hybrid system for scalable quantum computation. Quantum information is stored in long-lived hyperfine or rotational states of molecules which interact indirectly through resonant dipole-dipole interactions with Rydberg atoms. A two-qubit gate based on this interaction has a duration of 1 μs and an achievable fidelity of 99.9%. The gate has little sensitivity to the motional states of the particles – the molecules can be in thermal states, the atoms do not need to be trapped during Rydberg excitation, the gate does not heat the molecules, and heating of the atoms has a negligible effect. Within a large, static array, the gate can be applied to arbitrary pairs of molecules separated by tens of micrometres, making the scheme highly scalable. The molecule-atom interaction can also be used for rapid qubit initialization and efficient, non-destructive qubit readout, without driving any molecular transitions. Single qubit gates are driven using microwave pulses alone, exploiting the strong electric dipole transitions between rotational states. Thus, all operations required for large scale quantum computation can be done without moving the molecules or exciting them out of their ground electronic states.
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Journal articleFrasinski LJ, 2022,
Cumulant mapping as the basis of multi-dimensional spectrometry
, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 24, Pages: 20776-20787, ISSN: 1463-9076- Author Web Link
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- Citations: 2
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Journal articleZhao H, Knolle J, Moessner R, et al., 2022,
Suppression of Interband Heating for Random Driving
, PHYSICAL REVIEW LETTERS, Vol: 129, ISSN: 0031-9007- Author Web Link
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- Citations: 1
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Journal articleFerchaud C, Jarosch S, Avni T, et al., 2022,
Interaction of an intense few-cycle infrared laser pulse with an ultrathin transparent liquid sheet
, Optics Express, Vol: 30, Pages: 34684-34692, ISSN: 1094-4087We experimentally study the interaction between intense infrared few-cycle laser pulses and an ultrathin (∼2 µm) flat liquid sheet of isopropanol running in vacuum. We observe a rapid decline in transmission above a critical peak intensity of 50 TW/cm2 of the initially transparent liquid sheet, and the emission of a plume of material. We find both events are due to the creation of a surface plasma and are similar to processes observed in dielectric solids. After calculating the electron density for different laser peak intensities, we find an electron scattering rate of 0.3 fs-1 in liquid isopropanol to be consistent with our data. We study the dynamics of the plasma plume to find the expansion velocity of the plume front.
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Journal articlePont M, Albiero R, Thomas SE, et al., 2022,
Quantifying <i>n</i>-Photon Indistinguishability with a Cyclic Integrated Interferometer
, PHYSICAL REVIEW X, Vol: 12, ISSN: 2160-3308- Author Web Link
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- Citations: 1
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Journal articleVolksen F, Devlin JA, Borchert MJ, et al., 2022,
A high-Q superconducting toroidal medium frequency detection system with a capacitively adjustable frequency range >180 kHz
, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 93, ISSN: 0034-6748 -
Journal articleLiu W, Guo N-J, Yu S, et al., 2022,
Spin-active defects in hexagonal boron nitride
, Materials for Quantum Technology, Vol: 2, Pages: 032002-032002<jats:title>Abstract</jats:title> <jats:p>Quantum technology grown out of quantum information theory, including quantum communication, quantum computation and quantum sensing, not only provides powerful research tools for numerous fields, but also is expected to go to civilian use in the future. Solid-state spin-active defects are one of promising platforms for quantum technology, and the host materials include three-dimensional diamond and silicon carbide, and the emerging two-dimensional hexagonal boron nitride (hBN) and transition-metal dichalcogenides. In this review, we will focus on the spin defects in hBN, and summarize theoretical and experimental progresses made in understanding properties of these spin defects. In particular, the combination of theoretical prediction and experimental verification is highlighted. We also discuss the future advantages and challenges of solid-state spins in hBN on the path towards quantum information applications.</jats:p>
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Journal articleZhu YR, Joseph D, Ling C, et al., 2022,
Iterative quantum optimization with an adaptive problem Hamiltonian for the shortest vector problem
, PHYSICAL REVIEW A, Vol: 106, ISSN: 2469-9926- Author Web Link
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- Citations: 1
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Journal articleRuberti M, Patchkovskii S, Averbukh V, 2022,
Quantum coherence in molecular photoionization
, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 24, Pages: 19673-19686, ISSN: 1463-9076- Author Web Link
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- Citations: 6
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Journal articleMaimaris M, Pettipher AJ, Azzouzi M, et al., 2022,
Sub-10-fs observation of bound exciton formation in organic optoelectronic devices
, Nature Communications, Vol: 13, ISSN: 2041-1723Fundamental mechanisms underlying exciton formation in organic semiconductors are complex and elusive as it occurs on ultrashort sub-100-fs timescales. Some fundamental aspects of this process, such as the evolution of exciton binding energy, have not been resolved in time experimentally. Here, we apply a combination of sub-10-fs Pump-Push-Photocurrent, Pump-Push-Photoluminescence, and Pump-Probe spectroscopies to polyfluorene devices to track the ultrafast formation of excitons. While Pump-Probe is sensitive to the total concentration of excited states, Pump-Push-Photocurrent and Pump-Push-Photoluminescence are sensitive to bound states only, providing access to exciton binding dynamics. We find that excitons created by near-absorption-edge photons are intrinsically bound states, or become such within 10 fs after excitation. Meanwhile, excitons with a modest >0.3 eV excess energy can dissociate spontaneously within 50 fs before acquiring bound character. These conclusions are supported by excited-state molecular dynamics simulations and a global kinetic model which quantitatively reproduce experimental data.
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Journal articleLiu X, Wang W, Wright SC, et al., 2022,
The chemistry of AlF and CaF production in buffer gas sources.
, J Chem Phys, Vol: 157In this work, we explore the role of chemical reactions on the properties of buffer gas cooled molecular beams. In particular, we focus on scenarios relevant to the formation of AlF and CaF via chemical reactions between the Ca and Al atoms ablated from a solid target in an atmosphere of a fluorine-containing gas, in this case, SF6 and NF3. Reactions are studied following an ab initio molecular dynamics approach, and the results are rationalized following a tree-shaped reaction model based on Bayesian inference. We find that NF3 reacts more efficiently with hot metal atoms to form monofluoride molecules than SF6. In addition, when using NF3, the reaction products have lower kinetic energy, requiring fewer collisions to thermalize with the cryogenic helium. Furthermore, we find that the reaction probability for AlF formation is much higher than for CaF across a broad range of kinetic temperatures.
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