Quantum control papers on arXiv, selected and classified automatically by QOC. https://llorebaga.github.io/QOC/topics/pulse-parametrization/ 2026-07-17T00:00:00Z QOC https://arxiv.org/abs/2607.15915 2026-07-17T00:00:00Z 2026-07-17T00:00:00Z Julian K. DimitrovNikolay V. Vitanov

We propose a pulse-shaping method for improving population transfer in multistate stimulated Raman adiabatic passage (STIRAP) with nearest-neighbour couplings only. The method extends the quasiparallel-eigenenergy approach, previously used for two- and three-state systems, to multistate chains without introducing additional shortcut fields. The pump and Stokes fields are shaped so that the eigenenergies closest to the dark state remain nearly parallel to it during the central part of the interaction, where nonadiabatic transitions are most likely to occur. We derive analytic prescriptions for the required pulse shapes and apply them to five-, seven-, and nine-state chains formed by magnetic sublevels of degenerate manifolds with angular momenta $J_g\rightarrow J_e=J_g$ and $J_g\rightarrow J_e=J_g-1$ driven by a pair of right- and left-circularly polarized pulses. Numerical simulations show that the optimized pulses can reduce the population transfer error by several orders of magnitude compared to standard Gaussian pulses. The same shapes also improve robustness against variations of the peak Rabi frequency, the single-photon detuning, and the multiphoton detuning. The comparison between the two angular-momentum families shows that the $J_g\rightarrow J_g$ chains are generally more favourable, because their Clebsch-Gordan coefficients keep the relevant bright-state gap larger in the region where the dark state changes most rapidly. Finally, simulations with spontaneous emission show that the optimized resonant pulses remain advantageous in the lossy regime as well.

https://arxiv.org/abs/2605.04945 2026-05-06T00:00:00Z 2026-05-06T00:00:00Z Melvin StroblMaja FranzLukas SchellerEileen KuehnWolfgang MauererAchim Streit

In the domain of variational quantum algorithms, quantum Fourier models (QFMs) provide a mathematically well defined structure for quantum machine learning (QML). There has been a substantial amount of work on the scalability and trainability of such models showcasing the potential but also the limitations for the prospective application of QFMs. However, much less is known in the context of pulse-level quantum computing, where the microwave parameters that implement unitary operations on the hardware are used to perform computations directly instead of through the interface of quantum circuits. In this work, we evaluate QFMs through the lens of pulse parameters and link metrics such as expressibility and Fourier coefficient correlation (FCC) to this extended set of variational parameters. We show that while control over pulse shapes does not significantly alter the global expressibility or structural correlations of the Ansatz, it fundamentally alters the local optimisation landscape. For composite gates, independent pulse scalings replace a single logical angle by multiple independently tunable sub-angles. This relaxes the rigid monomial couplings induced by the gate-level parameterisation, and provides gradient descent with higher-dimensional escape routes, decoupling local parameter constraints and significantly boosting performance during training. Following an analytical proof, we show numerical results validating our theory on training a QFM with an exponential (ternary) feature map on a Fourier series with the same frequencies.

https://arxiv.org/abs/2604.21565 2026-04-23T00:00:00Z 2026-07-20T00:00:00Z Animesh PatraAnkur Raina

High-fidelity control of superconducting qubits requires carefully shaped microwave pulses to avoid several different kinds of error at once. This article is a pedagogical bridging text aimed at upper-level undergraduate and early graduate students who have completed an introductory quantum mechanics course and a first course in quantum computing or quantum information, but who have not yet encountered the physical implementation of qubit gates. We integrate physical intuition for pulse design, analytical gate-level descriptions, and practical hardware considerations into a single, derivation-driven narrative, with explicit learning objectives. We begin with simple pulse envelopes and their spectral properties, showing how finite bandwidth produces leakage outside the computational subspace. This motivates the derivative removal by adiabatic gate (DRAG) technique, which we derive explicitly using the Magnus expansion, obtaining a clear, order-by-order account of which physical error channel appears at which order and why DRAG's cancellation is necessarily incomplete. We discuss the practical hardware realities of control pulse generation, focusing on arbitrary waveform generators (AWG), local oscillators (LO), and IQ mixing. Finally, we extend the discussion to two-qubit operation via the cross-resonance gate, and interpret how driving the control qubit at the target qubit's transition frequency necessarily produces several unwanted interaction terms alongside the desired one, and how successive generations of pulse-engineering strategies have been designed to suppress them.

https://arxiv.org/abs/2603.11018 2026-03-11T00:00:00Z 2026-03-11T00:00:00Z Jaap J. WesdorpEric HyyppäJoona AnderssonJanos AdamRohit BeriwalVille BergholmSaga DahlSimone Diego FasciatiAlejandro Gomez FrieroZheming GaoDaria GusenkovaAndrew GuthrieJohannes HeinsooTuukka HiltunenKeiran HollandAmin HosseinkhaniSinan InelJoni IkonenShan W. JolinKristinn JuliussonSeung-Goo KimAnton KomlevRoope KokkoniemiOtto KoskinenJoonas KylmäläAlessandro LandraJulia LamprichMagdalena LehmuskoskiNizar LethifPer J. LiebermannTianyi LiAleksi LintunenFabian MarxerKunal MitraJakub MrożekLucas OrtegaMiha PapičMatti PartanenAlexander PlyushchStefan PogorzalekMichael RengerJussi RitvasSampo A. SaarinenIndrajeet SagarMatthew SarsbyMykhailo SavytskyiVille SelinmaaIvan TakmakovBrian TarasinskiFrancesca TostoDavid VaseyPanu VesanenJeroen VerjauwAlpo VälimaaNicola WurzHsiang-Sheng KuFrank DeppeJuha HasselCaspar Ockeloen-KorppiWei LiuJani TuorilaChun Fai ChanAttila GeresdiAntti Vepsäläinen

Single-qubit gates on superconducting quantum processors are typically implemented using microwave pulses applied through dedicated control lines. However, these microwave pulses may also drive other qubits due to crosstalk arising from capacitive coupling and wavefunction overlap in systems with closely spaced transition frequencies. Crosstalk and frequency crowding increase errors during simultaneous single-qubit operations relative to isolated gates, thus forming a major bottleneck for scaling superconducting quantum processors. In this work, we combine model-based qubit frequency optimization with pulse shaping to demonstrate crosstalk error mitigation in single-qubit gates on a 49-qubit superconducting quantum processor. We introduce and experimentally verify an analytical model of simultaneous single-qubit gate error caused by microwave crosstalk that depends on a given pulse shape. By employing a model-based optimization strategy of qubit frequencies, we minimize the crosstalk-induced error across the processor and achieve a mean simultaneous single-qubit gate fidelity of 99.96% for a 16-ns gate duration, approaching the mean individual gate fidelity. To further reduce the simultaneous error and required qubit frequency bandwidth on high-crosstalk qubit pairs, we introduce a crosstalk transition suppression (CTS) pulse shaping technique that minimizes the spectral energy around transitions inducing leakage and crosstalk errors. Finally, we combine CTS with model-based frequency optimization across the device and experimentally show a systematic reduction in the required qubit frequency bandwidth for high-fidelity simultaneous gates, supported by simulations of systems with up to 1000 qubits. By alleviating constraints on qubit frequency bandwidth for parallel single-qubit operations, this work represents an important step for scaling towards larger quantum processors.

https://arxiv.org/abs/2603.05417 2026-03-05T00:00:00Z 2026-03-05T00:00:00Z Valeriia BilokonElvira BilokonDenys I. Bondar

Quantum tracking control encodes the desired dynamics into a tailored driving field; here, we let the system find its own way there. We propose a real-time feedback control framework in which a proportional controller continuously corrects a simple transform-limited field based on the instantaneous mismatch between two systems' responses - producing the required control on the fly, without prior waveform design. The framework is demonstrated on two distinct examples: a single-active-electron atom, where hydrogen is driven to mimic argon's strong-field optical emission, and a Fermi-Hubbard chain, where a weakly interacting lattice reproduces the transport dynamics of a Mott-insulating reference. By shifting the control paradigm from predesigned inputs to adaptive response tracking, this approach establishes closed-loop feedback as a broadly applicable route to programmable quantum dynamics.

https://arxiv.org/abs/2602.22888 2026-02-26T00:00:00Z 2026-02-26T00:00:00Z Chun-Chi LinYang-Kai LueDung The Tran

We establish a rigorous existence theory for the quantum splines introduced by Brody, Holm, and Meier in Physical Review Letters (2012). These curves arise as solutions of a variational problem on the unitary group describing optimally controlled quantum evolutions. By formulating the problem within a geometric gradient flow framework for Riemannian spline interpolation, we construct a well-posed fourth order evolution whose asymptotic limits realize the desired quantum splines. The analysis requires adapting the variational structure to boundary conditions dictated by the physical model, which are not directly amenable to the setting in our recently developed framework for gradient flows of Riemannian spline interpolation. We show that, despite these difficulties, the modified system admits a rigorous analytical treatment, yielding both existence and a constructive procedure for generating quantum splines. Our results provide a mathematical foundation for the variational description of smooth quantum control trajectories and clarify the analytical structure underlying their formation.

https://arxiv.org/abs/2512.15301 2025-12-17T00:00:00Z 2025-12-17T00:00:00Z Yanhao SunJiayu MaXiangyu WangSong YuZiyang ChenHong Guo

Continuous-variable quantum key distribution (CV-QKD) enables two remote parties to establish information-theoretically secure keys and offers high practical feasibility due to its compatibility with mature coherent optical communication technologies. However, as CV-QKD systems progress toward digital implementations, device nonidealities drive the optical field from a single-mode to a continuous-mode region, thereby underscoring the mismatch between theoretical models and practical systems. Here, we introduce temporal modes to construct an entanglement-based scheme that more accurately captures device nonidealities and develop a corresponding secret key rate calculation method applicable to continuous-mode scenarios. We demonstrate that optimizing the pulse-shaping format can significantly improve performance under detector-bandwidth-limited conditions. Experimental results also confirm that the proposed model effectively describes the impact of sampling-time deviations. We further analyze a linear weighted-reconstruction digital signal processing method,which improves the secret key rate by approximately 50% in a 30-km fiber experiment without requiring additional hardware, demonstrating a substantial performance enhancement at metropolitan distances. The proposed theoretical framework accommodates a broader range of experimental conditions and can guide the optimization of digital CV-QKD systems.

https://arxiv.org/abs/2510.05905 2025-10-07T00:00:00Z 2026-09-26T00:00:00Z Jie LuJize HanJie-Dong HuangYang QianYing YanZhiguo Huang

Systematic Rabi-amplitude and detuning errors remain important sources of infidelity in high-fidelity quantum gates. We develop a robust pulse-engineering scheme for non-adiabatic holonomic quantum computing in a three-level $Λ$-type qutrit, combining inverse engineering with time-dependent perturbative analysis. Pulse shaping eliminates the leading second-order Rabi-amplitude contribution, while static detuning introduces a distinct population-mediated channel that cannot be removed within a single control loop. We therefore introduce a compensation loop that exactly cancels the dominant second-order $O_{13}^δ$ contribution, with the residual $O_{12}^δ$ channel further suppressed by pulse shaping. Using the logical average gate fidelity over the complete computational subspace, the optimized composite sequence reaches closed-system fidelities of $99.88\%$--$99.99\%$ for four representative single-qubit gates at $ε=0.2$ and $δ/2π=2$ MHz. With phenomenological decoherence at $T_1=T_2=30~μ{\rm s}$, the NOT and S gates retain fidelities of $99.72\%$ and $99.79\%$, respectively, with a coherence-time crossover near $0.58~μ{\rm s}$. These results identify the regime in which systematic-error suppression outweighs the decoherence cost of the additional control loop.

https://arxiv.org/abs/2509.05437 2025-09-05T00:00:00Z 2026-01-09T00:00:00Z Yang GaoFeiyu LiYang LiuZhen YangJiayu DingWuerkaixi NuerbolatiRuixia WangTang SuYanjun MaYirong JinHaifeng YuHe WangFei Yan

Quantum error correction protocols require rapid and repeated qubit measurements. While multiplexed readout in superconducting quantum systems improves efficiency, fast probe pulses introduce spectral broadening, leading to signal leakage into neighboring readout resonators. This crosstalk results in qubit dephasing and degraded readout fidelity. Here, we introduce a pulse shaping technique inspired by the derivative removal by adiabatic gate (DRAG) protocol to suppress measurement crosstalk during fast readout. By engineering a spectral notch at neighboring resonator frequencies, the method effectively mitigates spurious signal interference. Our approach integrates seamlessly with existing readout architectures, enabling fast, low-crosstalk multiplexed measurements without additional hardware overhead - a critical advancement for scalable quantum computing.

https://arxiv.org/abs/2508.02902 2025-08-04T00:00:00Z 2025-08-04T00:00:00Z İlker PolatRamon W. J. OverwaterMaximilian Rimbach-RussFabio Sebastiano

A fundamental challenge in quantum computing is to increase the number of operations within the qubit coherence time. While this can be achieved by decreasing the gate duration, the use of shorter signals increases their bandwidth and can cause leakage into energetically separated states. A common method to suppress leakage for short pulses is the Derivative Removal by Adiabatic Gate (DRAG) method, which however, relies on IQ modulation of radio-frequency (RF) signals, thus cannot be applied to the baseband signals, e.g., for semiconductor spin qubits. This paper proposes a novel technique, Delayed Leakage Reduction (DLR), that suppresses leakage at targeted frequencies even for baseband control by using time-delayed repetitions of the control signal to enable rapid, high-fidelity operations. We apply DLR on the adiabatic CZ gate between two spin qubits and achieve fidelities exceeding 99.9% within 9.4 ns for a resonance frequency difference of only 100 MHz. Towards the experimental realization of the proposed control method, we also assess the impact on the fidelity of the sampling rate of the electronic hardware generating the control pulse, thus setting the minimum hardware requirements for any experimental demonstration.

https://arxiv.org/abs/2506.19535 2025-06-24T00:00:00Z 2025-06-24T00:00:00Z Xueying MaiLiyun ZhangQinyang YuJunhua ZhangYao Lu

A central challenge in developing practical quantum processors is maintaining low control complexity while scaling to large numbers of qubits. Trapped-ion systems excel in small-scale operations and support rapid qubit scaling via long-chain architectures. However, their performance in larger systems is hindered by spectral crowding in radial motional modes, a problem that forces reliance on intricate pulse-shaping techniques to maintain gate fidelities. Here, we overcome this challenge by developing a novel trapped-ion processor with an individual-addressing system that generates steerable Hermite-Gaussian beam arrays. The transverse gradient of these beams couples qubits selectively to sparse axial motional modes, enabling to isolate a single mode as entanglement mediator. Leveraging this capability, we demonstrate addressable two-qubit entangling gates in chains up to six ions with fidelities consistently around 0.97, achieved without complex pulse shaping. Our method significantly reduces control overhead while preserving scalability, providing a crucial advance toward practical large-scale trapped-ion quantum computing.

https://arxiv.org/abs/2505.11071 2025-05-16T00:00:00Z 2025-12-17T00:00:00Z James WalklingMarin Bukov

Periodic kick drives are ubiquitous in digital quantum control, computation, and simulation, and are instrumental in studies of chaos and thermalization for their efficient representation through discrete gates. However, in the commonly used Fourier basis, kick drives lead to poor convergence of physical quantities. Instead, here we use the Walsh basis of periodic square-wave functions to describe the physics of periodic kick drives. In the strongly kicked regime, we find that it recovers Floquet dynamics of single- and many-body systems more accurately than the Fourier basis, due to the shape of the system's response in time. To understand this behavior, we derive an extended Sambe space formulation and an inverse-frequency expansion in the Walsh basis. We explain the enhanced performance within the framework of single-particle localization on the frequency lattice, where localization is correlated with small truncation errors. We show that strong hybridization between states of the kicked system and Walsh modes gives rise to Walsh polaritons that can be studied on digital quantum simulators. Our work lays the foundations of Walsh-Floquet theory, which is naturally implementable on digital quantum devices and suited to Floquet state manipulation using discrete gates.

https://arxiv.org/abs/2505.07726 2025-05-12T00:00:00Z 2025-05-12T00:00:00Z Svitlana MatsenkoAmirhossein GhazisaeidiMarcin JarzynaMikkel N. SchmidtSøren F. NielsenKonrad BanaszekDarko Zibar

Technical limitations in pulse shaping lead to mode mismatch, which significantly reduces the secure key rate in CV-QKD systems. To address this, a machine learning approach is employed to optimize the transmitter pulse-shape, effectively minimizing mode mismatch and yielding substantial performance improvements.

https://arxiv.org/abs/2503.21085 2025-03-27T00:00:00Z 2025-04-20T00:00:00Z Shengyong LiYidian FanXiang LiXinhui RuanQianchuan ZhaoZhihui PengRe-Bing WuJing ZhangPengtao Song

Quantum control requires high-precision and robust control pulses to ensure optimal system performance. However, control sequences generated with a system model may suffer from model bias, leading to low fidelity. While model-free reinforcement learning (RL) methods have been developed to avoid such biases, training an RL agent from scratch can be time-consuming, often taking hours to gather enough samples for convergence. This challenge has hindered the broad application of RL techniques to larger and more complex quantum control issues, limiting their adaptability. In this work, we use Reinforcement Learning from Demonstration (RLfD) to leverage the control sequences generated with system models and further optimize them with RL to avoid model bias. By avoiding learning from scratch and starting with reasonable control pulse shapes, this approach can increase sample efficiency by reducing the number of samples, which can significantly reduce the training time. Thus, this method can effectively handle pulse shapes that are discretized into more than 1000 pieces without compromising final fidelity. We have simulated the preparation of several high-fidelity non-classical states using the RLfD method. We also find that the training process is more stable when using RLfD. In addition, this method is suitable for fast gate calibration using reinforcement learning.

https://arxiv.org/abs/2501.18704 2025-01-30T00:00:00Z 2025-01-30T00:00:00Z P. CussenotB. GrivetBenjamin Peter LanyonT. E. NorthupHugues de RiedmattenAnders S. SorensenNicolas Sangouard

We present an architecture for remotely connecting cavity-coupled trapped ions via a quantum repeater based on rare-earth-doped crystals. The main challenge for its realization lies in interfacing these two physical platforms, which produce photons with a typical temporal mismatch of one or two orders of magnitude. To address this, we propose an efficient protocol that enables custom temporal reshaping of single-photon pulses whilst preserving purity. Our approach is to modify a commonly used memory protocol, called atomic frequency comb, for systems exhibiting inhomogeneous broadening like rare-earth-doped crystals. Our results offer a viable solution for uniting quantum processing nodes with a quantum repeater backbone.

https://arxiv.org/abs/2501.10710 2025-01-18T00:00:00Z 2025-09-11T00:00:00Z Ryo MatsudaRyutaro OhiraToshi SumidaHidehisa ShiomiAkinori MachinoShinichi MorisakaKeisuke KoikeTakefumi MiyoshiYoshinori KurimotoYuuya SugitaYosuke ItoYasunari SuzukiPeter A. SpringShiyu WangShuhei TamateYutaka TabuchiYasunobu NakamuraKazuhisa OgawaMakoto Negoro

In conventional architectures of superconducting quantum computers, each qubit is connected to its own control line, leading to a commensurate increase in the number of microwave lines as the system scales. Frequency-multiplexed qubit control addresses this problem by enabling multiple qubits to share a single microwave line. However, it can cause unwanted excitation of non-target qubits, especially when the detuning between qubits is smaller than the pulse bandwidth. Here, we propose a selective-excitation-pulse (SEP) technique that suppresses unwanted excitations by shaping a drive pulse to create null points at non-target qubit frequencies. In a proof-of-concept experiment with three fixed-frequency transmon qubits, we demonstrate that the SEP technique achieves single-qubit gate fidelities comparable to those obtained with conventional Gaussian pulses while effectively suppressing unwanted excitations in non-target qubits. These results highlight the SEP technique as a promising tool for enhancing frequency-multiplexed qubit control.

https://arxiv.org/abs/2412.17454 2024-12-23T00:00:00Z 2024-12-23T00:00:00Z Niklas J. GlaserFederico A. RoyIvan TsitsilinLeon KochNiklas BruckmoserJohannes SchirkJoão H. RomeiroGerhard B. P. HuberFlorian WallnerMalay SinghGleb KrylovAchim MarxLasse SödergrenChristian SchneiderMax WerninghausStefan Filipp

Achieving fast and high-fidelity qubit operations is crucial for unlocking the potential of quantum computers. In particular, reaching low gate errors in two-qubit gates has been a long-standing challenge in the field of superconducting qubits due to their typically long duration relative to coherence times. To realize fast gates, we utilize the hybridization between fixed-frequency superconducting qubits with a strongly interacting coupler mode that is tunable in frequency. To reduce population leakage during required adiabatic passages through avoided level crossings, we employ a sensitivity-adaptive closed-loop optimization method to design complex pulse shapes. We compare the performance of Gaussian-square, Fourier-series, and piecewise-constant-slope (PiCoS) pulse parametrizations and are able to reach 99.9 % controlled-Z gate fidelity using a 64 ns long Fourier-series pulse defined by only seven parameters. These high-fidelity values are achieved by analyzing the optimized pulse shapes to identify and systematically mitigate signal-line distortions in the experiment. To improve the convergence speed of the optimization we implement an adaptive cost function, which continuously maximizes the sensitivity. The demonstrated method can be used for tune-up and recalibration of superconducting quantum processors.

https://arxiv.org/abs/2410.08016 2024-10-10T00:00:00Z 2024-10-10T00:00:00Z Aruto HosakaMasaya TomitaYoshiaki TsujimotoShintaro NiimuraAkihito OmiKentaro WakuiMikio FujiwaraMasahiro TakeokaFumihiko Kannari

In this paper, we propose a novel method for interfering frequency-multiplexed photonic quantum states without the use of optical nonlinear effects, and experimentally demonstrate this technique via frequency-domain Hong-Ou-Mandel (HOM) interference. By cascading the generation of quantum states onto arbitrary orthogonal modes, we can induce interference across any desired frequency mode. Following the generation of quantum states onto the frequency modes, performing measurements in independent frequency bands enables the realisation of a frequency-domain linear optical circuit analogous to linear interference in the spatial domain. We successfully demonstrated programmable quantum interference by controlling the spectral mode functions and measurement bases. Our method offers a new approach to harness the full potential of light's temporal-frequency degrees of freedom, providing a path towards scalable and programmable photonic quantum computing architectures without the need for optical nonlinearities or spatial-mode beam splitters.

https://arxiv.org/abs/2409.13638 2024-09-20T00:00:00Z 2024-09-20T00:00:00Z Kaiyi WuLucas M. CohenKarthik V. MyilswamyNavin B. LingarajuHsuan-Hao LuJoseph M. LukensAndrew M. Weiner

We demonstrate spectral shaping of entangled photons with a six-channel microring-resonator-based silicon photonic pulse shaper. Through precise calibration of thermal phase shifters in a microresonator-based pulse shaper, we demonstrate line-by-line phase control on a 3~GHz grid for two frequency-bin-entangled qudits, corresponding to Hilbert spaces of up to $6\times 6$ ($3\times 3$) dimensions for shared (independent) signal-idler filters. The pulse shaper's fine spectral resolution enables control of nanosecond-scale temporal features, which are observed by direct coincidence detection of biphoton correlation functions that show excellent agreement with theory. This work marks, to our knowledge, the first demonstration of biphoton pulse shaping using an integrated spectral shaper and holds significant promise for applications in quantum information processing.

https://arxiv.org/abs/2408.05299 2024-08-09T00:00:00Z 2024-08-09T00:00:00Z Maxime Lapointe-MajorYongchao TangMehmet CanturkPooya Ronagh

Echoed conditional displacement (ECD) gates for bosonic systems have become the key element for real-time quantum error correction beyond the break-even point. These gates are characterized by a single complex parameter $β$, and can be constructed using Gaussian pulses and free evolutions with the help of an ancillary transmon qubit. We show that there is a lower bound for the gate time in the standard construction of an ECD gate. We present a method for optimizing the pulse shape of an ECD gate using a pulse-shaping technique subject to a set of experimental constraints. Our optimized pulse shapes remain symmetric, and can be applied to a range of target values of $β$ by tuning only the amplitude. We demonstrate that the total gate time of an ECD gate for a small value of $β$ can be reduced either by relaxing the no-overlap constraint on the primitives used in the standard construction or via our optimal-control method. We show a slight advantage of the optimal-control method by demonstrating a reduction in the preparation time of a $|+Z_\mathrm{GKP}>$ logical state by $\thicksim$$10\%$.

https://arxiv.org/abs/2405.20889 2024-05-31T00:00:00Z 2024-08-06T00:00:00Z Alice PaganoMatthias M. MüllerTommaso CalarcoSimone MontangeroPhila Rembold

Quantum Optimal Control (QOC) supports the advance of quantum technologies by tackling its problems at the pulse level: Numerical approaches iteratively work towards a given target by parametrising the applied time-dependent fields with a finite set of variables. The effectiveness of the resulting optimisation depends on the complexity of the problem and the number of variables. We consider different parametrisations in terms of basis functions, asking whether the choice of the applied basis affects the quality of the optimisation. Furthermore, we consider strategies to choose the most suitable basis. For the comparison, we test three different randomisable bases - introducing the sinc and sigmoid bases as alternatives to the Fourier basis - on QOC problems of varying complexity. For each problem, the basis-specific convergence rates result in a unique ranking. Especially for expensive evaluations, e.g., in closed-loop, a potential speed-up by a factor of up to 10 may be crucial for the optimisation's feasibility. We conclude that a problem-dependent basis choice is an influential factor for QOC efficiency and provide advice for its approach.

https://arxiv.org/abs/2404.17478 2024-04-26T00:00:00Z 2025-03-07T00:00:00Z Susanna KirchhoffFrank K. WilhelmFelix Motzoi

The Mølmer-Sørensen gate is a widely used entangling gate for ion platforms with inherent robustness to trap heating. The gate performance is limited by coherent errors, arising from the Lamb-Dicke (LD) approximation and sideband errors. Here, we provide explicit analytical formulas for errors up to fourth order in the LD parameter, by using the Magnus expansion to match numerical precision, and overcome significant, orders-of-magnitude underestimation of errors by previous theory methods. We show that fourth order Magnus expansion terms are unavoidable, being in fact leading order in LD, and are therefore critical to include for typical experimental fidelity ranges. We show how these errors can be dramatically reduced compared to previous theory by using analytical renormalization of the drive strength, by calibration of the Lamb-Dicke parameter, and by the use of smooth pulse shaping.

https://arxiv.org/abs/2403.01835 2024-03-04T00:00:00Z 2024-10-17T00:00:00Z Fabian RichterUlf SaalmannEnrico AllariaMatthias WollenhauptBenedetto ArdiniAlexander BrynesCarlo CallegariGiulio CerulloMiltcho DanailovAlexander DemidovichKatrin DulitzRaimund FeifelMichele Di FraiaSarang Dev GaneshamandiramLuca GiannessiNicolai GölzSebastian HartwegBernd von IssendorffTim LaarmannFriedemann LandmesserYilin LiMichele ManfreddaCristian ManzoniMoritz MichelbachArne MorlokMarcel MudrichAaron NgaiIvaylo NikolovNitish PalFabian PannekGiuseppe PencoOksana PlekanKevin C. PrinceGiuseppe SansoneAlberto SimoncigFrank StienkemeierRichard James SquibbPeter SusnjarMauro TrovoDaniel UhlBrendan WouterloodMarco ZangrandoLukas Bruder

Tailored light-matter interactions in the strong coupling regime enable the manipulation and control of quantum systems with up to unit efficiency, with applications ranging from quantum information to photochemistry. While strong light-matter interactions are readily induced at the valence electron level using long-wavelength radiation, comparable phenomena have been only recently observed with short wavelengths, accessing highly-excited multi-electron and inner-shell electron states. However, the quantum control of strong-field processes at short wavelengths has not been possible, so far, due to the lack of pulse shaping technologies in the extreme ultraviolet (XUV) and X-ray domain. Here, exploiting pulse shaping of the seeded free-electron laser (FEL) FERMI, we demonstrate the strong-field quantum control of ultrafast Rabi dynamics in helium atoms with high fidelity. Our approach unravels a strong dressing of the ionization continuum, otherwise elusive to experimental observables. The latter is exploited to achieve control of the total ionization rate, with prospective applications in many XUV and soft X-ray experiments. Leveraging recent advances in intense few-femtosecond to attosecond XUV to soft X-ray light sources, our results open an avenue to the efficient manipulation and selective control of core electron processes and electron correlation phenomena in real time.

https://arxiv.org/abs/2402.07887 2024-02-12T00:00:00Z 2025-11-19T00:00:00Z Mateusz KuniejPaweł MachnikowskiMichał Gawełczyk

State transfer between different quantum systems is key for successful quantum technologies. Over long distances, photons are irreplaceable, but on short ranges in miniaturized complex devices or hybrid systems, coupling via orders of magnitude shorter-wavelength acoustic waves has great potential. With interfaces to light, acoustic waves, and more, optically active quantum dots (QDs) are essential for multi-component systems. Here, we propose a hybrid acousto-optical method for non-resonant QD charge state control, extending the recent all-optical swing-up state preparation. We show that exciton and biexciton states, or other superpositions of charge states, can be prepared. Each field can act as a trigger, allowing for the implementation of either an optically gated acoustic control or the opposite scheme, where an optical pulse controls the transition during acoustic modulation. Thus, we introduce acoustic state control into a system that lacks direct acoustic coupling between the states. The method does not rely on pulse shaping and is expected to work with arbitrary pulse shapes as long as the optical dressing is performed quasi-adiabatically. Evaluating the phonon impact, we find an almost decoherence-free exciton preparation even at elevated temperatures with current QD and acoustic technology. This approach may also pave the way for optically controlled entanglement between emitters and acoustic modes, and further on-chip state transfer via quantum acoustic buses.

https://arxiv.org/abs/2303.01427 2023-03-02T00:00:00Z 2024-09-12T00:00:00Z Boxi LiTommaso CalarcoFelix Motzoi

While quantum circuits are reaching impressive widths in the hundreds of qubits, their depths have not been able to keep pace. In particular, cloud computing gates on multi-qubit, fixed-frequency superconducting chips continue to hover around the 1% error range, contrasting with the progress seen on carefully designed two-qubit chips, where error rates have been pushed towards 0.1%. Despite the strong impetus and a plethora of research, experimental demonstration of error suppression on these multi-qubit devices remains challenging, primarily due to the wide distribution of qubit parameters and the demanding calibration process required for advanced control methods. Here, we achieve this goal, using a simple control method based on multi-derivative, multi-constraint pulse shaping, which acts simultaneously against multiple error sources. Our approach establishes a two to fourfold improvement on the default calibration scheme, demonstrated on four qubits on the IBM Quantum Platform with limited and intermittent access, enabling these large-scale fixed-frequency systems to fully take advantage of their superior coherence times. The achieved CNOT fidelities of 99.7(1)% on those publically available qubits come from both coherent control error suppression and accelerated gate time.

https://arxiv.org/abs/2211.16241 2022-11-29T00:00:00Z 2022-11-29T00:00:00Z Maximilian Rimbach-RussStephan G. J. PhilipsXiao XueLieven M. K. Vandersypen

Semiconductor spin qubits demonstrated single-qubit gates with fidelities up to $99.9\%$ benchmarked in the single-qubit subspace. However, tomographic characterizations reveals non-negligible crosstalk errors in a larger space. Additionally, it was long thought that the two-qubit gate performance is limited by charge noise which couples to the qubits via the exchange interaction. Here, we show that coherent error sources such as a limited bandwidth of the control signals, diabaticity errors, microwave crosstalk, and non-linear transfer functions can equally limit the fidelity. We report a simple theoretical framework for pulse optimization that relates erroneous dynamics to spectral concentration problems and allows for the reuse of existing signal shaping methods on a larger set of gate operations. We apply this framework to common gate operations for spin qubits and show that simple pulse shaping techniques can significantly improve the performance of these gate operations in the presence of such coherent error sources. The methods presented in the paper were used to demonstrate two-qubit gate fidelities with $F>99.5\%$ in Ref.~[Xue et al, Nature 601, 343]. We also find that single and two-qubit gates can be optimized using the same pulse shape. We use analytic derivations and numerical simulations to arrive at predicted gate fidelities greater than $99.9\%$ with duration less than $4/(Δf)$ where $Δf$ is the difference in qubit frequencies.

https://arxiv.org/abs/2209.13173 2022-09-27T00:00:00Z 2022-09-27T00:00:00Z V. V. SoshenkoI. S. CojocaruS. V. BolshedvorskiiO. R. RubinasV. N. SorokinA. N. SmolyaninovA. V. Akimov

Nitrogen-vacancy centers possessing nuclear spins are promising candidates for a novel nuclear spin gyroscope. Preparation of a nuclear spin state is a crucial step to implement a sensor that utilizes a nuclear spin. In a low magnetic field, such a preparation utilizes population transfer, from polarized electronic spin to nuclear spin, using microwave pulses. The use of the narrowband microwave pulse proposed earlier is inefficient when magnetic transitions are not well resolved, particularly when applied to diamond with a natural abundance of carbon atoms or dense ensembles of nitrogen-vacancy centers. In this study, the authors performed optimization of the pulse shape for 3 relatively easily accessible pulse shapes. The optimization was done for a range of magnetic transition linewidths, corresponding to the practically important range of nitrogen concentrations (5-50 ppm). It was found that, while at low nitrogen concentrations, optimized pulse added very little to simple square shape pulse, and in the case of dense nitrogen-vacancy ensembles, with a rather wide magnetic transition width of 1.5 MHz optimal pulses, a factor of 15% improvement in the population of the target state was observed.

https://arxiv.org/abs/2206.03504 2022-06-07T00:00:00Z 2023-01-27T00:00:00Z Yasuo OdaDennis LucarelliKevin SchultzB. David CladerGregory Quiroz

We introduce a quantum control protocol that produces smooth, experimentally implementable control sequences optimized to combat temporally correlated noise for single qubit systems. The control ansatz is specifically chosen to be a functional expansion of discrete prolate spheroidal sequences, a discrete time basis known to be optimally concentrated in time and frequency, and quite attractive when faced with experimental control hardware constraints. We leverage the filter function formalism to transform the control problem into a filter design problem, and show that the frequency response of a quantum system can be carefully tailored to avoid the most relevant dynamical contributions of noise processes. Using gradient ascent, we obtain optimized filter functions and exploit them to elucidate important details about the relationship between filter function design, control bandwidth, and noise characteristics. In particular, we identify regimes of optimal noise suppression and in turn, optimal control bandwidth directly proportional to the size of the frequency bands where the noise power is large. In addition to providing guiding principles for filter design, our approach enables the development of controls that simultaneously yield robust noise filtering and high fidelity single qubit logic operations in a wide variety of complex noise environments.

https://arxiv.org/abs/2205.13097 2022-05-26T00:00:00Z 2022-05-26T00:00:00Z Kan TakaseAkito KawasakiByung Kyu JeongTakahiro KashiwazakiTakushi KazamaKoji EnbutsuKei WatanabeTakeshi UmekiShigehito MikiHirotaka TeraiMasahiro YabunoFumihiro ChinaWarit AsavanantMamoru EndoJun-ichi YoshikawaAkira Furusawa

Controlling the waveform of light is the key for a versatile light source in classical and quantum electronics. Although pulse shaping of classical light is a mature technique and has been used in various fields, more advanced applications would be realized by a light source that generates arbitrary quantum light with arbitrary temporal waveform. We call such a device a quantum arbitrary waveform generator (Q-AWG). The Q-AWG must be able to handle versatile quantum states of light, which are fragile. Thus, the Q-AWG requires a radically different methodology from classical pulse shaping. In this paper, we invent an architecture of Q-AWGs that can operate semi-deterministically at a repetition rate over GHz in principal. We demonstrate its core technology via generating highly non-classical states with waveforms that have never been realized before. This result would lead to powerful quantum technologies based on Q-AWGs such as practical optical quantum computing.

https://arxiv.org/abs/2203.07517 2022-03-14T00:00:00Z 2023-06-26T00:00:00Z Felix FehseM. DavidMichel Pioro-LadrièreW. A. Coish

Population-transfer schemes are commonly used to convert information robustly stored in some quantum system for manipulation and memory into more macroscopic degrees of freedom for measurement. These schemes may include, e.g., spin-to-charge conversion for spins in quantum dots, detuning of charge qubits between a noise-insensitive operating point and a measurement point, spatial shuttling of qubits encoded in spins or ions, and parity-to-charge conversion schemes for qubits based on Majorana zero modes. A common strategy is to use a slow (adiabatic) conversion. However, in an adiabatic scheme, the adiabaticity conditions, on the one hand, and accumulation of errors through dephasing, leakage, and energy relaxation processes on the other hand, limit the fidelity that can be achieved. Here, we give explicit fast quasiadiabatic (fast-QUAD) conversion strategies (pulse shapes) beyond the adiabatic approximation that allow for optimal state conversion. In contrast with many other approaches, here we account for noise in combination with pulse shaping. Although we restrict to noise sources that can be modeled by a classical fluctuating parameter, we allow generally for anisotropic nonGaussian noise that is nevertheless sufficiently weak to lead to a small error. Inspired by analytic methods that have been developed for dynamical decoupling theory, we provide a general framework for unique noise mitigation strategies that can be tailored to the system and environment of interest.