We demonstrate a substantial improvement in the spin-exchange gate using symmetric control instead of conventional detuning GaAs spin qubits, up to factor six increase quality gate. For operation, nanosecond voltage pulses are applied barrier that controls interdot potential between quantum dots, modulating exchange interaction while maintaining symmetry dots. Excellent agreement is found with model separately includes electrical and nuclear noise sources for both gating schemes. Unlike via...

Majorana bound states constitute one of the simplest examples emergent non-Abelian excitations in condensed matter physics. A toy model proposed by Kitaev shows that such can arise at ends a spinless $p$-wave superconducting chain. Practical proposals for its realization require coupling neighboring quantum dots chain via both electron tunneling and crossed Andreev reflection. While processes have been observed semiconducting nanowires carbon nanotubes, crossed-Andreev interaction was...

Conditional-phase (cz) gates in transmons can be realized by flux pulsing computational states towards resonance with noncomputational ones. We present a 40 ns cz gate based on bipolar pulse suppressing leakage (0.1%) interference and approaching the speed limit set exchange coupling. This harnesses built-in echo to enhance fidelity (99.1%) is robust long-timescale distortion flux-control line, ensuring repeatability. Numerical simulations matching experiment show that limited high-frequency...

We present conductance-matrix measurements of a three-terminal superconductor-semiconductor hybrid device consisting two normal leads and one superconducting lead. Using symmetry decomposition the conductance, we find that antisymmetric components pairs local nonlocal conductances qualitatively match at energies below gap, compare this finding with relations based on noninteracting scattering matrix approach. Further, charge character Andreev bound states is extracted from...

Using a singlet-triplet spin qubit as sensitive spectrometer of the GaAs nuclear bath, we demonstrate that spectrum Overhauser noise agrees with classical diffusion model over 6 orders magnitude in frequency, from 1 mHz to kHz, is flat below 10 mHz, and falls 1/f^{2} for frequency f≳1 Hz. Increasing applied magnetic field 0.1 0.75 T suppresses electron-mediated diffusion, which decreases spectral content region lowers saturation each by an order magnitude, consistent numerical model....

End-to-end correlated bound states are investigated in superconductor-semiconductor hybrid nanowires at zero magnetic field. Peaks subgap conductance independently identified from each wire end, and a cross-correlation function is computed that counts end-to-end coincidences, averaging over thousands of features. Strong correlations short, 300-nm device reduced by factor 4 long, 900-nm device. In addition, distributions investigated, between the left right based on their mutual information.

The Heisenberg exchange interaction between neighboring quantum dots allows precise voltage control over spin dynamics, due to the ability precisely overlap of orbital wavefunctions by gate electrodes. This study fundamental electronic phenomena and finds applications in information processing. Although spin-based circuits based on short-range interactions are possible, development scalable, longer-range coupling schemes constitutes a critical challenge within spin-qubit community....

We systematically study three-terminal InSb-Al nanowire devices by using radio-frequency reflectometry. Tunneling spectroscopy measurements on both ends of the hybrid nanowires are performed while varying chemical potential, magnetic field and junction transparencies. Identifying lowest-energy state allows for construction lowest- zero-energy diagrams, which show how states evolve as a function aforementioned parameters. Importantly, comparing diagrams taken each end hybrids enables...

We operate a resonant exchange qubit in highly symmetric triple-dot configuration using IQ-modulated RF pulses. At the resulting three-dimensional sweet spot splitting is an order of magnitude less sensitive to all relevant control voltages, compared conventional operating point, but we observe no significant improvement quality Rabi oscillations. For weak driving this consistent with Overhauser field fluctuations modulating splitting. strong infer that effective voltage noise modulates...

We investigate the spin of a multielectron GaAs quantum dot in sequence nine charge occupancies, by exchange coupling to neighboring two-electron double dot. For all we make use leakage spectroscopy technique reconstruct spectrum states vicinity interdot transition between single- and In same regime also perform time-resolved measurements coherent oscillations With these measurements, identify distinct characteristics state, depending on whether dot's occupancy is even or odd. three out four...

We use a one-electron quantum dot as spectroscopic probe to study the spin properties of gate-controlled multielectron GaAs at transition between odd and even occupation numbers. observe that ground-state transitions from spin-1/2-like singletlike tripletlike we increase detuning towards next higher charge state. The sign reversal in inferred exchange energy persists zero magnetic field, strength is tunable by gate voltages in-plane fields. Complementing leakage spectroscopy data, inspection...

For mesoscopic quantum devices, efficient characterization and high-fidelity readout using only microwave resonators is of great practical interest, especially to investigate the large parameter space frequently occurring in semiconducting devices. This work shows how dc conductance measurements can be substituted with rf through implementation gigahertz-frequency resonators. It also demonstrates multiplexed dispersive gate sensing, which detects electron hybridization high sensitivity,...

Utilizing dispersive gate sensing (DGS), we investigate the spin-orbit field (${\mathbf{B}}_{\mathrm{SO}}$) orientation in a many-electron double quantum dot (DQD) defined an $\mathrm{In}\mathrm{Sb}$ nanowire. While characterizing interdot tunnel couplings, find measured signal depends on electron-charge occupancy, as well amplitude and of external magnetic field. The is mostly insensitive to when DQD occupied by total odd number electrons. For even electrons, reduced finite aligns with...

Cooper pair splitters hold utility as a platform for investigating the entanglement of electrons in pairs, but probing with voltage-biased Ohmic contacts prevents retention from split pairs since they can escape to drain reservoirs. We report ability controllably and retain single multi-quantum-dot device isolated lead reservoirs, separately demonstrate technique detecting emerging pair. First, we identify coherent splitting charge transition using dispersive gate sensing at GHz frequencies....

Radio-frequency (RF) reflectometry is implemented in hybrid semiconductor-superconductor nanowire systems designed to probe Majorana zero modes. Two approaches are presented. In the first, nanowire-based devices part of a resonant circuit, allowing conductance be measured as function several gate voltages ~40 times faster than using conventional low-frequency lock-in methods. second, capacitively coupled nearby RF single-electron transistor made from separate nanowire, detection charge,...

The filter function formalism quantitatively describes the dephasing of a qubit by bath that causes Gaussian fluctuations in energies with an arbitrary noise power spectrum. Here, we extend this to account for more general types couple through terms do not commute qubit's bare Hamiltonian. Our approach applies any spectrum generates slow evolution. We demonstrate our case singlet-triplet qubits subject both quasistatic nuclear and $1/{\ensuremath{\omega}}^{\ensuremath{\alpha}}$ charge find...

We introduce Cryoscope, a method for sampling on-chip baseband pulses used to dynamically control qubit frequency in quantum processor. specifically use Cryoscope measure the step response of dedicated flux lines two-junction transmon qubits circuit QED processors with temporal resolution room-temperature arbitrary waveform generator producing pulses. As first application, we iteratively improve this using optimized real-time digital filters counter linear-dynamical distortion line, as...

Quantum interference of electron tunneling occurs in any system where multiple paths connect states. This unavoidably arises two-dimensional semiconducting qubit arrays, and must be controlled as a prerequisite for the manipulation readout hybrid topological parity qubits. Studying loop formed by two quantum dots, we demonstrate magnetic-flux-tunable hybridization between electronic levels, an irreducibly simple is expected to occur. Using radio-frequency reflectometry dots’ gate electrodes...

We study single-electron charging events in an Al/InAs nanowire hybrid system with deliberately introduced gapless regions. The occupancy of a Coulomb island is detected using nearby radio-frequency quantum dot as charge sensor. demonstrate that 1 micron gapped segment the wire can be used to efficiently suppress single electron poisoning region and therefore protect parity while maintaining good electrical contact normal lead. In absence protection by energy, 1e switching rate reduced below...

We demonstrate the use of radio-frequency (rf) resonators to measure capacitance nanoscale semiconducting devices in field-effect transistor configurations. The rf resonator is attached gate or lead device. Consequently, tuning carrier density conducting channel device affects resonance frequency, quantitatively reflecting its capacitance. test measurement method on InSb and InAs nanowires at dilution-refrigerator temperatures. measured capacitances are consistent with those inferred from...

We present a model of two Anderson impurities coupled to and through superconducting island. The parametrizes the strength coupling between impurity sites, allowing it represent variable distance impurities. systematically explore effect parameters in subspaces with total even odd occupancy, identifying unique features charge stability diagrams that distinguish parities. For electron parity, we identify device tuning, which splitting lowest energy states is highly insensitive changes...

A simple, single-color method for permanent marking of the position individual self-assembled semiconductor Quantum Dots (QDs) at cryogenic temperatures is reported. The combines in situ photolithography with standard micro-photoluminescence spectroscopy. Its utility proven by a systematic magnetooptical study single CdTe/ZnTe QD containing Mn2+ ion, where magnetic field up to 10 T two orthogonal, Faraday and Voigt, configurations applied same QD. presented approach can be wide range solid...

We study a hybrid device defined in an InAs nanowire with epitaxial Al shell that consists of quantum dot contact superconducting island. The is electrically floating, prohibiting transport measurements, but providing access to states would otherwise be highly excited and unstable. Radio-frequency reflectometry lumped-element resonators couples capacitatively the dot, detects presence discrete subgap states. perform detailed case no island states, quantum-dot-induced controlled by tunnel...