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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 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 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 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 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 articleSauvage F, Mintert F, 2022,
Optimal Control of Families of Quantum Gates
, PHYSICAL REVIEW LETTERS, Vol: 129, ISSN: 0031-9007- Author Web Link
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- Citations: 4
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Journal articleLi Z-P, Wang Y-T, Yu S, et al., 2022,
Experimental investigation of high-efficiency weak-value amplification of nonunitary evolution
, PHYSICAL REVIEW A, Vol: 106, ISSN: 2469-9926 -
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- Author Web Link
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- Citations: 2
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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- Author Web Link
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- Citations: 3
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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- Author Web Link
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- Citations: 2
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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: 10
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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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Working paperSun B, Morozko F, Salter PS, et al., 2022,
On-chip beam rotators, polarizers and adiabatic mode converters through low-loss waveguides with variable cross-sections
, Publisher: ArXivPhotonics 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.
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Working paperSempere-Llagostera S, Patel RB, Walmsley IA, et al., 2022,
Experimentally finding dense subgraphs using a time-bin encoded Gaussian boson sampling device
, Publisher: ArxivGaussian 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.
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Journal articleJoseph D, Martinez AJ, Ling C, et al., 2022,
Quantum mean-value approximator for hard integer-value problems
, PHYSICAL REVIEW A, Vol: 105, ISSN: 2469-9926- Author Web Link
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- Citations: 1
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Journal articleAlexander R, Gvirtz-Chen S, Jennings D, 2022,
Infinitesimal reference frames suffice to determine the asymmetry properties of a quantum system
, New Journal of Physics, Vol: 24, ISSN: 1367-2630Symmetry principles are fundamental in physics, and while they are well understood within Lagrangian mechanics, their impact on quantum channels has a range of open questions. The theory of asymmetry grew out of information-theoretic work on entanglement and quantum reference frames, and allows us to quantify the degree to which a quantum system encodes coordinates of a symmetry group. Recently, a complete set of entropic conditions was found for asymmetry in terms of correlations relative to infinitely many quantum reference frames. However, these conditions are difficult to use in practice and their physical implications unclear. In the present theoretical work, we show that this set of conditions has extensive redundancy, and one can restrict to reference frames forming any closed surface in the state space that has the maximally mixed state in its interior. This in turn implies that asymmetry can be reduced to just a single entropic condition evaluated at the maximally mixed state. Contrary to intuition, this shows that we do not need macroscopic, classical reference frames to determine the asymmetry properties of a quantum system, but instead infinitesimally small frames suffice. Building on this analysis, we provide simple, closed conditions to estimate the minimal depolarization needed to make a given quantum state accessible under channels covariant with any given symmetry group.
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Journal articleThekkadath G, Sempere-Llagostera S, Bell B, et al., 2022,
Experimental demonstration of Gaussian boson sampling with displacement
, PRX Quantum, Vol: 3, ISSN: 2691-3399Gaussian 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.
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Journal articleKoukoulekidis N, Jennings D, 2022,
Constraints on magic state protocols from the statistical mechanics of Wigner negativity
, NPJ QUANTUM INFORMATION, Vol: 8- Author Web Link
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- Citations: 6
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Journal articleGirling M, Cirstoiu C, Jennings D, 2022,
Estimation of correlations and non-separability in quantum channels via unitarity benchmarking
, Physical Review Research, Vol: 4, ISSN: 2643-1564The ability to transfer quantum information between systems is a fundamental component of quantum technologies and leads to correlations within the global quantum process. However, correlation structures in quantum channels are less studied than those in quantum states. Motivated by recent techniques in randomized benchmarking, we develop a range of results for efficient estimation of correlations within a bipartite quantum channel. We introduce subunitarity measures that are invariant under local changes of basis, generalize the unitarity of a channel, and allow for the analysis of quantum information exchange within channels. Using these, we show that unitarity is monogamous, and we provide an information-disturbance relation. We then define a notion of correlated unitarity that quantifies the correlations within a given channel. Crucially, we show that this measure is strictly bounded on the set of separable channels and therefore provides a witness of nonseparability. Finally, we describe how such measures for effective noise channels can be efficiently estimated within different randomized benchmarking protocols. We find that the correlated unitarity can be estimated in a SPAM-robust manner for any separable quantum channel, and we show that a benchmarking/tomography protocol with mid-circuit resets can reliably witness nonseparability for sufficiently small reset errors. The tools we develop provide information beyond that obtained via simultaneous randomized benchmarking and so could find application in the analysis of cross-talk errors in quantum devices.
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Journal articleSong W, Lim Y, Jeong K, et al., 2022,
Quantum solvability of noisy linear problems by divide-and-conquer strategy
, Quantum Science and Technology, Vol: 7, ISSN: 2058-9565Noisy 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.
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Journal articleBarrett TJ, Evans W, Gadge A, et al., 2022,
An environmental monitoring network for quantum gas experiments and devices
, Quantum Science and Technology, Vol: 7Quantum technology is approaching a level of maturity, recently demonstrated in space-borne experiments and in-field measurements, which would allow for adoption by non-specialist users. Parallel advancements made in microprocessor-based electronics and database software can be combined to create robust, versatile and modular experimental monitoring systems. Here, we describe a monitoring network used across a number of cold atom laboratories with a shared laser system. The ability to diagnose malfunction, unexpected or unintended behavior and passively collect data for key experimental parameters, such as vacuum chamber pressure, laser beam power, or resistances of important conductors, significantly reduces debugging time. This allows for efficient control over a number of experiments and remote control when access is limited.
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Journal articleZhang C, Zhang C, Cheng L, et al., 2022,
Inner-shell excitation in the YbF molecule and its impact on laser cooling
, Journal of Molecular Spectroscopy, Vol: 386, ISSN: 0022-2852The 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 ๐ด2๐ฑ1โ2 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 ๐ด2๐ฑ1โ2 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 ๐ด2๐ฑ1โ2 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, ๐2๐ด+. We use electronic structure calculations to characterize the 4f hole states and the strengthsof transitions between these states and the ๐ด2๐ฑ1โ2 and ๐2๐ด+ 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.
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Working paperKoukoulekidis N, Jennings D, 2022,
Constraints on magic state protocols from the statistical mechanics of Wigner negativity
, Publisher: Nature ResearchMagic states are key ingredients in schemes to realize universalfault-tolerant quantum computation. Theories of magic states attempt toquantify this computational element via monotones and determine how thesestates may be efficiently transformed into useful forms. Here, we develop astatistical mechanical framework based on majorization to describe Wignernegative magic states for qudits of odd prime dimension processed underClifford circuits. We show that majorization allows us to both quantifydisorder in the Wigner representation and derive upper bounds for magicdistillation. These bounds are shown to be tighter than other bounds, such asfrom mana and thauma, and can be used to incorporate hardware physics, such astemperature dependence and system Hamiltonians. We also show that a subset ofsingle-shot R\'{e}nyi entropies remain well-defined on quasi-distributions, arefully meaningful in terms of data processing and can acquire negative valuesthat signal magic. We find that the mana of a magic state is the measure ofdivergence of these R\'{e}nyi entropies as one approaches the Shannon entropyfor Wigner distributions, and discuss how distillation lower bounds could beobtained in this setting. This use of majorization for quasi-distributionscould find application in other studies of non-classicality, and raises novelquestions in the context of classical statistical mechanics.
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Journal articleWill C, Bohman M, Driscoll T, et al., 2022,
Sympathetic cooling schemes for separately trapped ions coupled via image currents
, NEW JOURNAL OF PHYSICS, Vol: 24, ISSN: 1367-2630 -
Journal articleSchofield RC, Burdekin P, Fasoulakis A, et al., 2022,
Narrow and Stable Single Photon Emission from Dibenzoterrylene in <i>para</i>-Terphenyl Nanocrystals
, CHEMPHYSCHEM, Vol: 23, ISSN: 1439-4235- Author Web Link
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- Citations: 1
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Journal articleAyuso Molinero D, Ordonez AF, Decleva P, et al., 2022,
Strong chiral response in non-collinear high harmonic generation driven by purely electric-dipole interactions
, Optics Express, Vol: 30, ISSN: 1094-4087High harmonic generation (HHG) records the ultrafast electronic response of matter to light, encoding key properties of the interrogated quantum system, such as chirality. The first implementation of chiral HHG [Cireasa et al, Nat. Phys. 11, 654 (2015) [CrossRef] ] relied on the weak electronic response of a medium of randomly oriented chiral molecules to the magnetic component of an elliptically polarized wave, yielding relatively weak chiro-optical signals. Here we apply state-of-the-art semi-analytical modelling to show that elliptically polarized light can drive a strong chiral response in chiral molecules via purely electric-dipole interactions – the magnetic component of the wave does not participate at all. This strong chiro-optical response, which remains hidden in standard HHG experiments, can be mapped into the macroscopic far-field signal using a non-collinear configuration, creating new opportunities for imaging chiral matter and chiral dynamics on ultrafast time scales.
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