A5013227303- Quantum Information and Cryptography
- Quantum and electron transport phenomena
- Quantum Computing Algorithms and Architecture
- Physics of Superconductivity and Magnetism
- Quantum Mechanics and Applications
- Mechanical and Optical Resonators
- Spectroscopy and Quantum Chemical Studies
- Cold Atom Physics and Bose-Einstein Condensates
- Advanced Thermodynamics and Statistical Mechanics
- Quantum optics and atomic interactions
- Semiconductor Quantum Structures and Devices
- Laser-Matter Interactions and Applications
- Quantum many-body systems
- Advancements in Semiconductor Devices and Circuit Design
- Neural Networks and Reservoir Computing
- Surface and Thin Film Phenomena
- Quantum Electrodynamics and Casimir Effect
- Photonic and Optical Devices
- Atomic and Subatomic Physics Research
- Nonlinear Dynamics and Pattern Formation
- Superconductivity in MgB2 and Alloys
- Metamaterials and Metasurfaces Applications
- Magnetic and transport properties of perovskites and related materials
- Quantum chaos and dynamical systems
- Semiconductor materials and devices
Forschungszentrum Jülich
2021-2025
Saarland University
2016-2025
University of Glasgow
2019
University of Waterloo
2007-2016
European Synchrotron Radiation Facility
2015
Ludwig-Maximilians-Universität München
2002-2010
University of California, Santa Barbara
2010
Regroupement Québécois sur les Matériaux de Pointe
2009
Université de Sherbrooke
2009
Delft University of Technology
2000-2008
Microwave spectroscopy experiments have been performed on two quantum levels of a macroscopic superconducting loop with three Josephson junctions. Level repulsion the ground state and first excited is found where classical persistent-current states opposite polarity are degenerate, indicating symmetric antisymmetric superpositions states. The persistent currents 0.5 microampere correspond to center-of-mass motion millions Cooper pairs.
In realizations of quantum computing, a two-level system (qubit) is often singled out from the many levels an anharmonic oscillator. these cases, simple qubit control fails on short time scales because coupling to leakage levels. We provide easy implement analytic formula that inhibits this any single-control analog or pixelated pulse. It based adding second proportional derivative first. For realistic parameters superconducting qubits, strategy reduces error by order magnitude relative...
It is control that turns scientific knowledge into useful technology: in physics and engineering it provides a systematic way for driving dynamical system from given initial state desired target with minimized expenditure of energy resources. As one the cornerstones enabling quantum technologies, optimal keeps evolving expanding areas as diverse quantum-enhanced sensing, manipulation single spins, photons, or atoms, optical spectroscopy, photochemistry, magnetic resonance (spectroscopy well...
Within the last two decades, Quantum Technologies (QT) have made tremendous progress, moving from Noble Prize award-winning experiments on quantum physics into a cross-disciplinary field of applied research. are being developed now that explicitly address individual states and make use 'strange' properties, such as superposition entanglement. The comprises four domains: Communication, Simulation, Computation, Sensing Metrology. One success factor for rapid advancement QT is well-aligned...
Abstract Quantum optimal control, a toolbox for devising and implementing the shapes of external fields that accomplish given tasks in operation quantum device best way possible, has evolved into one cornerstones enabling technologies. The last few years have seen rapid evolution expansion field. We review here recent progress our understanding controllability open systems development application control techniques to also address key challenges sketch roadmap future developments.
In qubits made from a weakly anharmonic oscillator the leading source of error at short gate times is leakage population out two dimensional Hilbert space that forms qubit. this article we develop general scheme based on an adiabatic expansion to find pulse shapes correct type error. We family solutions allows tailoring what practical implement for specific application. Our result contains and improves previously developed derivative removal by technique [F. Motzoi et al., Phys. Rev. Lett....
We describe a microwave photon counter based on the current-biased Josephson junction. The junction is tuned to absorb single photons from incident field, after which it tunnels into classically observable voltage state. Using two such detectors, we have performed version of Hanbury Brown--Twiss experiment at 4 GHz and demonstrated clear signature bunching for thermal source. design readily scalable tens parallelized junctions, configuration that would allow number-resolved counting photons.
Abstract Reaching high-speed, high-fidelity qubit operations requires precise control over the shape of underlying pulses. For weakly anharmonic systems, such as superconducting transmon qubits, short gates lead to leakage states outside computational subspace. Control pulses designed with open-loop optimal may reduce leakage. However, model inaccuracies can severely limit usability We implemented a closed-loop optimization that simultaneously adapts all parameters based on measurements cost...
We carry out an extensive experimental and theoretical study of the Josephson effect in S-N-S junctions made a diffusive normal metal (N) embedded between two superconducting electrodes (S). Our experiments are performed on Nb-Cu-Nb with highly-transparent interfaces. give predictions quasiclassical theory various regimes precise quantitative level. describe crossover short long junction provide temperature dependence critical current using dimensionless units $eR_{N}I_{c}/\epsilon_{c}$...
We introduce a systematic formalism for two-resonator circuit QED, where two on-chip microwave resonators are simultaneously coupled to one superconducting qubit. Within this framework, we demonstrate that the qubit can function as quantum switch between resonators, which assumed be originally independent. In three-circuit network, mediates geometric second-order interaction otherwise decoupled resonators. dispersive regime, it also gives rise dynamic perturbative interaction. The and...
Quantum computation places very stringent demands on gate fidelities, and experimental implementations require both the controls resultant dynamics to conform hardware-specific constraints. Superconducting qubits present additional requirement that pulses must have simple parameterizations, so they can be further calibrated in experiment, compensate for uncertainties system parameters. Other quantum technologies, such as sensing, extremely high fidelities. We a novel, conceptually...
A central challenge for implementing quantum computing in the solid state is decoupling qubits from intrinsic noise of material. We investigate implementation gates a paradigmatic, non-Markovian model: single-qubit coupled to two-level system that exposed heat bath. systematically search optimal pulses using generalization novel open systems gradient ascent pulse engineering algorithm. Next known bias point this model, there are which lead high-fidelity operations wide range decoherence parameters.
We describe an approach to the integrated control and measurement of a large-scale superconducting multiqubit array comprising up 108 physical qubits using proximal coprocessor based on Single Flux Quantum (SFQ) digital logic family. Coherent is realized by irradiating directly with classical bitstreams derived from optimal theory. Qubit performed Josephson photon counter, which provides access result projective quantum at millikelvin stage. analyze power budget footprint SFQ discuss...
Optimal quantum control theory carries a huge promise for technology. Its experimental application, however, is often hindered by imprecise knowledge of the input variables, system's parameters. We show how to overcome this adaptive hybrid optimal control, using protocol named Ad-HOC. This combines open- and closed-loop first performing gradient search towards near-optimal pulse then an fidelity estimation with gradient-free method. For typical settings in solid-state information processing,...
Quantum chemistry is an important area of application for quantum computation. In particular, algorithms applied to the electronic structure problem promise exact, efficient methods determination energy atoms and molecules. The Bravyi–Kitaev transformation a method mapping occupation state fermionic system onto qubits. This maps Hamiltonian n interacting fermions ‐local improvement in locality over Jordan–Wigner transformation, which results O ( )‐local qubit Hamiltonian. We present detail,...
Efforts to scale-up quantum computation have reached a point where the principal limiting factor is not number of qubits, but entangling gate infidelity. However, highly detailed system characterization required understand underlying error sources an arduous process and impractical with increasing chip size. Open-loop optimal control techniques allow for improvement gates are limited by models they based on. To rectify situation, we provide integrated open-source tool-set Control,...
In a mesoscopic superconductor--normal metal--superconductor ( $\mathrm{SNS}$) heterostructure the quasiparticle distribution can be driven far from equilibrium by voltage applied across normal metal. This reduces supercurrent between superconducting electrodes, which creates possibility of using these $\mathrm{SNS}$ junctions as fast switches and transistors. We describe system in framework quasiclassical theory find good agreement with recent experiments. propose further experimental...
Quantum optimal control theory is applied to two and three coupled Josephson charge qubits. It shown that by using shaped pulses a CNOT gate can be obtained with trace fidelity > 0.99999 for the qubits, even when including higher states, leakage below 1%. Yet, required time only fifth of pioneering experiment [T. Yamamoto et al., Nature 425 (2003), 941] otherwise identical parameters. The controls have palindromic smooth courses representable superpositions few harmonics. We outline schemes...
In this article, we develop a numerical method to find optimal control pulses that accounts for the separation of timescales between variation input fields and applied Hamiltonian. traditional optimization methods, these are treated as being same. While approximation has had much success, in applications where controls filtered substantially or mixed with fast carrier, resulting optimized have little relation physical fields. Our technique remains numerically efficient dimension our search...
Many techniques in quantum control rely on frequency separation as a means for suppressing unwanted couplings. In its simplest form, the mechanism relies low bandwidth of pulses long duration. Here we perform higher-order quantum-mechanical treatment that allows higher precision and shorter times. particular, identify three kinds off-resonant effects: (i) simultaneous driven couplings (e.g., due to drive crosstalk), (ii) additional (initially undriven) transitions such those an infinite...
We show that the use of shaped pulses improves fidelity a Rydberg blockade two-qubit entangling gate by several orders magnitude compared to previous protocols based on square or optimal control pulses. Using analytical Derivative Removal Adiabatic Gate (DRAG) reduce excitation primary leakage states and an method finding we generate Bell with $F>0.9999$ in 300 K environment for time only $50\;{\rm ns}$, which is order faster than protocols. These results establish potential neutral atom...
Recent experimental work on superconducting transmon qubits in 3D cavities show that their coherence times are increased by an order of magnitude compared to 2D cavity counterparts. However take advantage these while scaling up the number it is advantageous address individual which all coupled same fields. The challenge controlling this system comes from spectral crowding, where leakage transition close computational transitions other. Here shown fast pulses possible single using two...