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  • Journal article
    Ruberti M, Patchkovskii S, Averbukh V, 2022,

    Quantum coherence in molecular photoionization

    , PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 24, Pages: 19673-19686, ISSN: 1463-9076
  • Journal article
    Maimaris M, Pettipher AJ, Azzouzi M, Walke DJ, Zheng X, Gorodetsky A, Dong Y, Tuladhar Shakya P, Crespo H, Nelson J, Tisch J, Bakulin Aet al., 2022,

    Sub-10-fs observation of bound exciton formation in organic optoelectronic devices

    , Nature Communications, Vol: 13, ISSN: 2041-1723

    Fundamental 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.

  • Journal article
    Liu X, Wang W, Wright SC, Doppelbauer M, Meijer G, Truppe S, Pérez-Ríos Jet al., 2022,

    The chemistry of AlF and CaF production in buffer gas sources.

    , J Chem Phys, Vol: 157

    In 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.

  • Journal article
    Tarrant J, Khokhlova M, Averbukh V, 2022,

    Interferometry of quantum revivals

    , JOURNAL OF CHEMICAL PHYSICS, Vol: 157, ISSN: 0021-9606
  • Journal article
    Sauvage F, Mintert F, 2022,

    Optimal Control of Families of Quantum Gates

    , PHYSICAL REVIEW LETTERS, Vol: 129, ISSN: 0031-9007
  • Journal article
    Li Z-P, Wang Y-T, Yu S, Liu W, Meng Y, Yang Y-Z, Wang Z-A, Guo N-J, Zeng X-D, Tang J-S, Li C-F, Guo G-Cet al., 2022,

    Experimental investigation of high-efficiency weak-value amplification of nonunitary evolution

    , PHYSICAL REVIEW A, Vol: 106, ISSN: 2469-9926
  • Journal article
    Ma 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: 1050-2947

    The 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.

  • Journal article
    Kanari-Naish LA, Clarke J, Qvarfort S, Vanner MRet al., 2022,

    Two-mode Schrodinger-cat states with nonlinear optomechanics: generation and verification of non-Gaussian mechanical entanglement

  • Journal article
    Danilov D, Tran T, Bearpark MJJ, Marangos JPP, Worth GAA, Robb MAAet 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 article
    Garratt D, Misiekis L, Wood D, Larsen E, Matthews M, Alexander O, Ye P, Jarosch S, Ferchaud C, Struber C, Johnson A, Bakulin A, Penfold T, Marangos Jet al., 2022,

    Direct observation of ultrafast exciton localization in an organic semiconductor with soft X-ray transient absorption spectroscopy

    , Nature Communications, Vol: 13, ISSN: 2041-1723

    The 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.

  • Journal article
    Zhao H, Mintert F, Knolle J, Moessner Ret al., 2022,

    Localization persisting under aperiodic driving

    , PHYSICAL REVIEW B, Vol: 105, ISSN: 2469-9950
  • Journal article
    Schwickert D, Ruberti M, Kolorenc P, Usenko S, Przystawik A, Baev K, Baev I, Braune M, Bocklage L, Czwalinna MK, Deinert S, Duesterer S, Hans A, Hartmann G, Haunhorst C, Kuhlmann M, Palutke S, Roehlsberger R, Roensch-Schulenburg J, Schmidt P, Toleikis S, Viefhaus J, Martins M, Knie A, Kip D, Averbukh V, Marangos JP, Laarmann Tet al., 2022,

    Electronic quantum coherence in glycine molecules probed with ultrashort x-ray pulses in real time

    , SCIENCE ADVANCES, Vol: 8, ISSN: 2375-2548
  • Journal article
    Cao N, Xie J, Zhang A, Hou S-Y, Zhang L, Zeng Bet 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>

  • Journal article
    Chevalier H, Kwon H, Khosla KE, Pikovski I, Kim MSet al., 2022,

    Many-body probes for quantum features of spacetime

    , AVS Quantum Science, Vol: 4, Pages: 1-10, ISSN: 2639-0213

    Many 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.

  • Working paper
    Sun B, Morozko F, Salter PS, Moser S, Pong Z, Patel RB, Walmsley IA, Hazan A, Barré N, Jesacher A, Fells J, Katiyi A, Novitsky A, Karabchevsky A, Booth MJet al., 2022,

    On-chip beam rotators, polarizers and adiabatic mode converters through low-loss waveguides with variable cross-sections

    , Publisher: ArXiv

    Photonics integrated circuitry would benefit considerably from the ability toarbitrarily control waveguide cross-sections with high precision and low loss,in order to provide more degrees of freedom in manipulating propagating light.Here, we report on a new optical-fibres-compatible glass waveguide byfemtosecond laser writing, namely spherical phase induced multi-core waveguide(SPIM-WG), which addresses this challenging task with three dimensional on-chiplight control. Precise deformation of cross-sections is achievable along thewaveguide, with shapes and sizes finely controllable of high resolution in bothhorizontal and vertical transversal directions. We observed that thesewaveguides have high refractive index contrast of 0.017, low propagation lossof 0.14 dB/cm, and very low coupling loss of 0.19 dB coupled from a single modefibre. SPIM-WG devices were easily fabricated that were able to perform on-chipbeam rotation through varying angles, or manipulate polarization state ofpropagating light for target wavelengths. We also demonstrated SPIM-WG modeconverters that provide arbitrary adiabatic mode conversion with highefficiency between symmetric and asymmetric non-uniform modes; examples includecircular, elliptical modes and asymmetric modes from ppKTP waveguides which aregenerally applied in frequency conversion and quantum light sources. Createdinside optical glass, these waveguides and devices have the capability tooperate across ultra-broad bands from visible to infrared wavelengths. Thecompatibility with optical fibre also paves the way toward packaged photonicintegrated circuitry, which usually needs input and output fibre connections.

  • Working paper
    Sempere-Llagostera S, Patel RB, Walmsley IA, Kolthammer WSet al., 2022,

    Experimentally finding dense subgraphs using a time-bin encoded Gaussian boson sampling device

    , Publisher: Arxiv

    Gaussian Boson Sampling (GBS) is a quantum computing concept based on drawingsamples from a multimode nonclassical Gaussian state using photon-numberresolving detectors. It was initially posed as a near-term approach aiming toachieve quantum advantage, but several applications have been proposed eversince, such as the calculation of graph features or molecular vibronic spectra,among others. For the first time, we use a time-bin encoded interferometer toimplement GBS experimentally and extract samples to enhance the search fordense subgraphs in a graph. Our results indicate an improvement over classicalmethods for subgraphs of sizes three and four in a graph containing ten nodes.In addition, we numerically explore the role of imperfections in the opticalcircuit and on the performance of the algorithm.

  • Journal article
    Walter N, Seifert J, Truppe S, Schewe HC, Sartakov BG, Meijer Get al., 2022,

    Spectroscopic characterization of singlet-triplet doorway states of aluminum monofluoride.

    , J Chem Phys, Vol: 156

    Aluminum monofluoride (AlF) possesses highly favorable properties for laser cooling, both via the A1Π and a3Π states. Determining efficient pathways between the singlet and the triplet manifold of electronic states will be advantageous for future experiments at ultralow temperatures. The lowest rotational levels of the A1Π, v = 6 and b3Σ+, v = 5 states of AlF are nearly iso-energetic and interact via spin-orbit coupling. These levels thus have a strongly mixed spin-character and provide a singlet-triplet doorway. We here present a hyperfine resolved spectroscopic study of the A1Π, v = 6//b3Σ+, v = 5 perturbed system in a jet-cooled, pulsed molecular beam. From a fit to the observed energies of the hyperfine levels, the fine and hyperfine structure parameters of the coupled states and their relative energies as well as the spin-orbit interaction parameter are determined. The standard deviation of the fit is about 15 MHz. We experimentally determine the radiative lifetimes of selected hyperfine levels by time-delayed ionization, Lamb dip spectroscopy, and accurate measurements of the transition lineshapes. The measured lifetimes range between 2 and 200 ns, determined by the degree of singlet-triplet mixing for each level.

  • Journal article
    Joseph D, Martinez AJ, Ling C, Mintert Fet al., 2022,

    Quantum mean-value approximator for hard integer-value problems

    , PHYSICAL REVIEW A, Vol: 105, ISSN: 2469-9926
  • Journal article
    Thekkadath G, Sempere-Llagostera S, Bell B, Patel R, Kim M, Walmsley Iet al., 2022,

    Experimental demonstration of Gaussian boson sampling with displacement

    , PRX Quantum, Vol: 3, ISSN: 2691-3399

    Gaussian boson sampling (GBS) is a quantum sampling task in which one has to draw samples from the photon-number distribution of a large-dimensional nonclassical squeezed state of light. In an effort to make this task intractable for a classical computer, experiments building GBS machines have mainly focused on increasing the dimensionality and squeezing strength of the nonclassical light. However, no experiment has yet demonstrated the ability to displace the squeezed state in phase space, which is generally required for practical applications of GBS. In this work, we build a GBS machine that achieves the displacement by injecting a laser beam alongside a two-mode squeezed vacuum state into a 15-mode interferometer. We focus on two new capabilities. Firstly, we use the displacement to reconstruct the multimode Gaussian state at the output of the interferometer. Our reconstruction technique is in situ and requires only three measurement settings regardless of the state dimension. Secondly, we study how the addition of classical laser light in our GBS machine affects the complexity of sampling its output photon statistics. We introduce and validate approximate semiclassical models that reduce the computational cost when a significant fraction of the detected light is classical.

  • Journal article
    Doppelbauer M, Wright SC, Hofsäss S, Sartakov BG, Meijer G, Truppe Set al., 2022,

    Hyperfine-resolved optical spectroscopy of the A2Π ← X2Σ+ transition in MgF.

    , J Chem Phys, Vol: 156

    We report on hyperfine-resolved laser spectroscopy of the A2Π ← X2Σ+ transition of magnesium monofluoride (MgF), relevant for laser cooling. We recorded 25 rotational transitions with an absolute accuracy of better than 20 MHz, assigned 56 hyperfine lines, and determined precise rotational, fine, and hyperfine structure parameters for the A2Π state. The radiative lifetime of the A2Π state was determined to be 7.2(3) ns, in good agreement with ab initio calculations. The transition isotope shift between bosonic isotopologues of the molecule is recorded and compared to predicted values within the Born-Oppenheimer approximation. We measured the Stark effect of selected rotational lines of the A2Π ← X2Σ+ transition by applying electric fields of up to 10.6 kV cm-1 and determined the permanent electric dipole moments of 24MgF in its ground X2Σ+ and first excited A2Π states to be μX = 2.88(20) D and μA = 3.20(22) D, respectively. Based on these measurements, we caution for potential losses from the optical cycling transition due to electric field induced parity mixing in the excited state. In order to scatter 104 photons, the electric field must be controlled to below 1 V cm-1.

  • Journal article
    Barrett TJ, Evans W, Gadge A, Bhumbra S, Sleegers S, Shah R, Fekete J, Orucevic F, Kruger Pet al., 2022,

    An environmental monitoring network for quantum gas experiments and devices

  • Journal article
    Song W, Lim Y, Jeong K, Ji Y-S, Lee J, Kim J, Kim MS, Bang Jet al., 2022,

    Quantum solvability of noisy linear problems by divide-and-conquer strategy

    , Quantum Science and Technology, Vol: 7, ISSN: 2058-9565

    Noisy linear problems have been studied in various science and engineering disciplines. A class of 'hard' noisy linear problems can be formulated as follows: Given a matrix $\hat{A}$ and a vector b constructed using a finite set of samples, a hidden vector or structure involved in b is obtained by solving a noise-corrupted linear equation $\hat{A}\mathbf{x}\approx \mathbf{b}+\boldsymbol{\eta }$, where η is a noise vector that cannot be identified. For solving such a noisy linear problem, we consider a quantum algorithm based on a divide-and-conquer strategy, wherein a large core process is divided into smaller subprocesses. The algorithm appropriately reduces both the computational complexities and size of a quantum sample. More specifically, if a quantum computer can access a particular reduced form of the quantum samples, polynomial quantum-sample and time complexities are achieved in the main computation. The size of a quantum sample and its executing system can be reduced, e.g., from exponential to sub-exponential with respect to the problem length, which is better than other results we are aware. We analyse the noise model conditions for such a quantum advantage, and show when the divide-and-conquer strategy can be beneficial for quantum noisy linear problems.

  • Journal article
    Zhang C, Zhang C, Cheng L, Steimle TC, Tarbutt MRet al., 2022,

    Inner-shell excitation in the YbF molecule and its impact on laser cooling

    , Journal of Molecular Spectroscopy, Vol: 386, ISSN: 0022-2852

    The YbF molecule is a sensitive system for measuring the electron’s electric dipole moment. The precision ofthis measurement can be improved by direct laser cooling of the molecules to ultracold temperature. However,low-lying electronic states arising from excitation of a 4f electron may hinder laser cooling. One set of these ‘‘4fhole’’ states lies below the 𝐴2𝛱1∕2 excited state used for laser cooling, and radiative decay to these intermediatelevels, even with branching ratios as small as 10−5, can be a hindrance. Other 4f hole states lie very close tothe 𝐴2𝛱1∕2 state, and a perturbation results in states of mixed character that are involved in the laser coolingcycle. This perturbation may enhance the loss of molecules to states outside of the laser cooling cycle. Wemodel the perturbation of the 𝐴2𝛱1∕2 state to determine the strength of the coupling between the states, thede-perturbed potential energy curves, and the radiative branching ratios to various vibrational levels of theground state, 𝑋2𝛴+. We use electronic structure calculations to characterize the 4f hole states and the strengthsof transitions between these states and the 𝐴2𝛱1∕2 and 𝑋2𝛴+ states. We identify a leak out of the cooling cyclewith a branching ratio of roughly 5 × 10−4, dominated by the contribution of the ground state configurationin a 4f hole state. Finally, we assess the impact of these results for laser cooling of YbF and molecules withsimilar structure.

  • Journal article
    Walter N, Doppelbauer M, Marx S, Seifert J, Liu X, Pérez-Ríos J, Sartakov BG, Truppe S, Meijer Get al., 2022,

    Spectroscopic characterization of the a3Π state of aluminum monofluoride.

    , J Chem Phys, Vol: 156

    Spectroscopic studies of aluminum monofluoride (AlF) have revealed its highly favorable properties for direct laser cooling. All Q lines of the strong A1Π ← X1Σ+ transition around 227 nm are rotationally closed and thereby suitable for the main cooling cycle. The same holds for the narrow, spin-forbidden a3Π ← X1Σ+ transition around 367 nm, which has a recoil limit in the µK range. We here report on the spectroscopic characterization of the lowest rotational levels in the a3Π state of AlF for v = 0-8 using a jet-cooled, pulsed molecular beam. An accidental AC Stark shift is observed on the a3Π0, v = 4 ← X1Σ+, v = 4 band. By using time-delayed ionization for state-selective detection of the molecules in the metastable a3Π state at different points along the molecular beam, the radiative lifetime of the a3Π1, v = 0, J = 1 level is experimentally determined as τ = 1.89 ± 0.15 ms. A laser/radio frequency multiple resonance ionization scheme is employed to determine the hyperfine splittings in the a3Π1, v = 5 level. The experimentally derived hyperfine parameters are compared to the outcome of quantum chemistry calculations. A spectral line with a width of 1.27 kHz is recorded between hyperfine levels in the a3Π, v = 0 state. These measurements benchmark the electronic potential of the a3Π state and yield accurate values for the photon scattering rate and for the elements of the Franck-Condon matrix of the a3Π-X1Σ+ system.

  • Journal article
    Will C, Bohman M, Driscoll T, Wiesinger M, Abbass F, Borchert MJ, Devlin JA, Erlewein S, Fleck M, Latacz B, Moller R, Mooser A, Popper D, Wursten E, Blaum K, Matsuda Y, Ospelkaus C, Quint W, Walz J, Smorra C, Ulmer Set al., 2022,

    Sympathetic cooling schemes for separately trapped ions coupled via image currents

    , NEW JOURNAL OF PHYSICS, Vol: 24, ISSN: 1367-2630
  • Journal article
    Schofield RC, Burdekin P, Fasoulakis A, Devanz L, Bogusz DP, Hoggarth RA, Major KD, Clark ASet al., 2022,

    Narrow and Stable Single Photon Emission from Dibenzoterrylene in <i>para</i>-Terphenyl Nanocrystals

    , CHEMPHYSCHEM, Vol: 23, ISSN: 1439-4235
  • Journal article
    Karra M, Cretu MT, Friedrich B, Truppe S, Meijer G, Pérez-Ríos Jet al., 2022,

    Dynamics of translational and rotational thermalization of AlF molecules via collisions with cryogenic helium

    , Physical Review A, Vol: 105, ISSN: 2469-9926
  • Journal article
    Tang H, Banchi L, Wang T-Y, Shang X-W, Tan X, Zhou W-H, Feng Z, Pal A, Li H, Hu C-Q, Kim MS, Jin X-Met al., 2022,

    Generating Haar-uniform randomness using stochastic quantum walks on a photonic chip

    , Physical Review Letters, Vol: 128, ISSN: 0031-9007

    As random operations for quantum systems are intensively used in various quantum information tasks, a trustworthy measure of the randomness in quantum operations is highly demanded. The Haar measure of randomness is a useful tool with wide applications, such as boson sampling. Recently, a theoretical protocol was proposed to combine quantum control theory and driven stochastic quantum walks to generate Haar-uniform random operations. This opens up a promising route to converting classical randomness to quantum randomness. Here, we implement a two-dimensional stochastic quantum walk on the integrated photonic chip and demonstrate that the average of all distribution profiles converges to the even distribution when the evolution length increases, suggesting the 1-pad Haar-uniform randomness. We further show that our two-dimensional array outperforms the one-dimensional array of the same number of waveguide for the speed of convergence. Our Letter demonstrates a scalable and robust way to generate Haar-uniform randomness that can provide useful building blocks to boost future quantum information techniques.

  • Journal article
    Li S, Driver T, Rosenberger P, Champenois EG, Duris J, Al-Haddad A, Averbukh V, Barnard JCT, Berrah N, Bostedt C, Bucksbaum PH, Coffee RN, DiMauro LF, Fang L, Garratt D, Gatton A, Guo Z, Hartmann G, Haxton D, Helml W, Huang Z, LaForge AC, Kamalov A, Knurr J, Lin M-F, Lutman AA, MacArthur JP, Marangos JP, Nantel M, Natan A, Obaid R, O'Neal JT, Shivaram NH, Schori A, Walter P, Li Wang A, Wolf TJA, Zhang Z, Kling MF, Marinelli A, Cryan JPet al., 2022,

    Attosecond coherent electron motion in Auger-Meitner decay

    , SCIENCE, Vol: 375, Pages: 285-+, ISSN: 0036-8075
  • Journal article
    Moroney N, Del Bino L, Zhang S, Woodley MTM, Hill L, Wildi T, Wittwer VJ, Sudmeyer T, Oppo G-L, Vanner MR, Brasch V, Herr T, Del'Haye Pet al., 2022,

    A Kerr polarization controller


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