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Journal articleRego L, Smirnova O, Ayuso Molinero D, 2023,
Tilting light's polarization plane to spatially separate the ultrafast nonlinear response of chiral molecules
, Nanophotonics, ISSN: 2192-8606 -
Journal articleCheng C, Frasinski LJ, Moğol G, et al., 2023,
Multiparticle Cumulant Mapping for Coulomb Explosion Imaging.
, Phys Rev Lett, Vol: 130We extend covariance velocity map ion imaging to four particles, establishing cumulant mapping and allowing for measurements that provide insights usually associated with coincidence detection, but at much higher count rates. Without correction, a fourfold covariance analysis is contaminated by the pairwise correlations of uncorrelated events, but we have addressed this with the calculation of a full cumulant, which subtracts pairwise correlations. We demonstrate the approach on the four-body breakup of formaldehyde following strong field multiple ionization in few-cycle laser pulses. We compare Coulomb explosion imaging for two different pulse durations (30 and 6 fs), highlighting the dynamics that can take place on ultrafast timescales. These results have important implications for Coulomb explosion imaging as a tool for studying ultrafast structural changes in molecules, a capability that is especially desirable for high-count-rate x-ray free-electron laser experiments.
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Journal articleHo C, Lim J, Sauer B, et al., 2023,
Measuring the nuclear magnetic quadrupole moment in heavy polar molecules
, Frontiers in Physics, Vol: 11, Pages: 1-10, ISSN: 2296-424XTheories that extend the Standard Model of particle physics often introduce new interactions that violate charge-parity (CP) symmetry. CP-violating effects within an atomic nucleus can be probed by measuring its nuclear magnetic quadrupole moment (MQM). The sensitivity of such a measurement is enhanced when using a heavy polar molecule containing a nucleus with quadrupole deformation. We determine how the energy levels of a molecule are shifted by the MQM and how those shifts can be measured. The measurement scheme requires molecules in a superposition of magnetic sub-levels that differ by many units of angular momentum. We develop a generic scheme for preparing these states. Finally, we consider the sensitivity that can be reached, showing that this method can reduce the current uncertainties on several CP-violating parameters.
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Journal articleHaug T, Kim M, 2023,
Scalable measures of magic for quantum computers
, PRX Quantum, Vol: 4, ISSN: 2691-3399Nonstabilizerness or magic resource characterizes the amount of non-Clifford operations needed to prepare quantum states. It is a crucial resource for quantum computing and a necessary condition for quantum advantage. However, quantifying magic resource beyond a few qubits has been a major challenge. Here, we introduce efficient measures of magic resource for pure quantum states with a sampling cost that is independent of the number of qubits. Our method uses Bell measurements over two copies of a state, which we implement in experiment together with a cost-free error-mitigation scheme. We show the transition of classically simulable stabilizer states into intractable quantum states on the IonQ quantum computer. For applications, we efficiently distinguish stabilizer and nonstabilizer states with low measurement cost even in the presence of experimental noise. Further, we propose a variational quantum algorithm to maximize our measure via the shift rule. Our algorithm can be free of barren plateaus even for highly expressible variational circuits. Finally, we experimentally demonstrate a Bell-measurement protocol for the stabilizer Rényi entropy as well as the Wallach-Meyer entanglement measure. Our results pave the way to understanding the nonclassical power of quantum computers, quantum simulators, and quantum many-body systems.
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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 -
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, 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 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 articleZhao H, Knolle J, Moessner R, et al., 2022,
Suppression of Interband Heating for Random Driving
, PHYSICAL REVIEW LETTERS, Vol: 129, ISSN: 0031-9007 -
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 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 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, 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 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 articleTarrant J, Khokhlova M, Averbukh V, 2022,
Interferometry of quantum revivals
, JOURNAL OF CHEMICAL PHYSICS, Vol: 157, ISSN: 0021-9606- 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: 1
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Journal articleSauvage F, Mintert F, 2022,
Optimal Control of Families of Quantum Gates
, PHYSICAL REVIEW LETTERS, Vol: 129, ISSN: 0031-9007 -
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 -
Journal articleMa Y, Pace MCC, Kim MS, 2022,
Unifying the sorensen-molmer gate and the milburn gate with an optomechanical example
, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 106, ISSN: 1050-2947The Sørensen-Mølmer gate and Milburn gate are two geometric phase gates, generating nonlinear self-interaction of a target mode via its interaction with an auxiliary mechanical mode, in the continuous- and pulsed-interaction regimes, respectively. In this paper we aim at unifying the two gates by demonstrating that the Sørensen-Mølmer gate is the continuous limit of the Milburn gate, emphasizing the geometrical interpretation in the mechanical phase space. We explicitly consider imperfect gate parameters, focusing on relative errors in time for the Sørensen-Mølmer gate and in phase angle increment for the Milburn gate. We find that, although the purities of the final states increase for the two gates upon reducing the interaction strength together with traversing the mechanical phase space multiple times, the fidelities behave differently. We point out that the difference exists because the interaction strength depends on the relative error when taking the continuous limit from the pulsed regime, thereby unifying the mathematical framework of the two gates. We demonstrate this unification in the example of an optomechanical system, where mechanical dissipation is also considered. We highlight that the unified framework facilitates our method of deriving the dynamics of the continuous-interaction regime without solving differential equations.
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Journal articleKanari-Naish LA, Clarke J, Qvarfort S, et al., 2022,
Two-mode Schrodinger-cat states with nonlinear optomechanics: generation and verification of non-Gaussian mechanical entanglement
, QUANTUM SCIENCE AND TECHNOLOGY, Vol: 7, ISSN: 2058-9565 -
Journal articleDanilov D, Tran T, Bearpark MJJ, et al., 2022,
How electronic superpositions drive nuclear motion following the creation of a localized hole in the glycine radical cation
, JOURNAL OF CHEMICAL PHYSICS, Vol: 156, ISSN: 0021-9606 -
Journal articleGarratt D, Misiekis L, Wood D, et al., 2022,
Direct observation of ultrafast exciton localization in an organic semiconductor with soft X-ray transient absorption spectroscopy
, Nature Communications, Vol: 13, ISSN: 2041-1723The localization dynamics of excitons in organic semiconductors influence the efficiency of charge transfer and separation in these materials. Here we apply time-resolved X-ray absorption spectroscopy to track photoinduced dynamics of a paradigmatic crystalline conjugated polymer: poly(3-hexylthiophene) (P3HT) commonly used in solar cell devices. The π→π* transition, the first step of solar energy conversion, is pumped with a 15 fs optical pulse and the dynamics are probed by an attosecond soft X-ray pulse at the carbon K-edge. We observe X-ray spectroscopic signatures of the initially hot excitonic state, indicating that it is delocalized over multiple polymer chains. This undergoes a rapid evolution on a sub 50 fs timescale which can be directly associated with cooling and localization to form either a localized exciton or polaron pair.
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Journal articleZhao H, Mintert F, Knolle J, et al., 2022,
Localization persisting under aperiodic driving
, PHYSICAL REVIEW B, Vol: 105, ISSN: 2469-9950 -
Journal articleSchwickert D, Ruberti M, Kolorenc P, et al., 2022,
Electronic quantum coherence in glycine molecules probed with ultrashort x-ray pulses in real time
, SCIENCE ADVANCES, Vol: 8, ISSN: 2375-2548- Author Web Link
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- Citations: 6
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Journal articleCao N, Xie J, Zhang A, et al., 2022,
Neural networks for quantum inverse problems
, New Journal of Physics, Vol: 24, Pages: 063002-063002<jats:title>Abstract</jats:title> <jats:p>Quantum inverse problem (QIP) is the problem of estimating an unknown quantum system from a set of measurements, whereas the classical counterpart is the inverse problem of estimating a distribution from a set of observations. In this paper, we present a neural-network-based method for QIPs, which has been widely explored for its classical counterpart. The proposed method utilizes the quantumness of the QIPs and takes advantage of the computational power of neural networks to achieve remarkable efficiency for the quantum state estimation. We test the method on the problem of maximum entropy estimation of an unknown state <jats:italic>ρ</jats:italic> from partial information both numerically and experimentally. Our method yields high fidelity, efficiency and robustness for both numerical experiments and quantum optical experiments.</jats:p>
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Journal articleChevalier H, Kwon H, Khosla KE, et al., 2022,
Many-body probes for quantum features of spacetime
, AVS Quantum Science, Vol: 4, Pages: 1-10, ISSN: 2639-0213Many theories of quantum gravity can be understood as imposing a minimum length scale the signatures of which can potentially be seen in precise table top experiments. In this work, we inspect the capacity for correlated many-body systems to probe non-classicalities of spacetime through modifications of the commutation relations. We find an analytic derivation of the dynamics for a single mode light field interacting with a single mechanical oscillator and with coupled oscillators to first order corrections to the commutation relations. Our solution is valid for any coupling function as we work out the full Magnus expansion. We numerically show that it is possible to have superquadratic scaling of a nonstandard phase term, arising from the modification to the commutation relations, with coupled mechanical oscillators.
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