8 research outputs found
Dynamical Polarization of the Fermion Parity in a Nanowire Josephson Junction
No full textJosephson junctions in InAs nanowires proximitized with an Al shell can host gate-tunable Andreev bound states. Depending on the bound state occupation, the fermion parity of the junction can be even or odd. Coherent control of Andreev bound states has recently been achieved within each parity sector, but it is impeded by incoherent parity switches due to excess quasiparticles in the superconducting environment. Here, we show that we can polarize the fermion parity dynamically using microwave pulses by embedding the junction in a superconducting LC resonator. We demonstrate polarization up to 94%±1% (89%±1%) for the even (odd) parity as verified by single shot parity readout. Finally, we apply this scheme to probe the flux-dependent transition spectrum of the even or odd parity sector selectively, without any postprocessing or heralding.QRD/Kouwenhoven LabQN/Wimmer GroupBUS/Quantum Delf
Singlet-doublet transitions of a quantum dot Josephson junction detected in a transmon circuit
No full textWe realize a hybrid superconductor-semiconductor transmon device in which the Josephson effect is controlled by a gate-defined quantum dot in an InAs-Al nanowire. Microwave spectroscopy of the transition spectrum of the transmon allows us to probe the ground-state parity of the quantum dot as a function of the gate voltages, the external magnetic flux, and the magnetic field applied parallel to the nanowire. The measured parity phase diagram is in agreement with that predicted by a single-impurity Anderson model with superconducting leads. Through continuous-time monitoring of the circuit, we furthermore resolve the quasiparticle dynamics of the quantum dot Josephson junction across the phase boundaries. Our results can facilitate the realization of semiconductor-based 0-pi qubits and Andreev qubits
Microwave spectroscopy of interacting Andreev spins
No full textAndreev bound states are fermionic states localized in weak links between superconductors which can be occupied with spinful quasiparticles. Microwave experiments using superconducting circuits with InAs/Al nanowire Josephson junctions have recently enabled probing and coherent manipulation of Andreev states but have remained limited to zero or small magnetic fields. Here, we use a flux-tunable superconducting circuit compatible in magnetic fields up to 1T to perform spectroscopy of spin-polarized Andreev states up to ∼250mT, beyond which the spectrum becomes gapless. We identify singlet and triplet states of two quasiparticles occupying different Andreev states through their dispersion in magnetic field. These states are split by exchange interaction and couple via spin-orbit coupling, analogously to two-electron states in quantum dots. We also show that the magnetic field allows to drive a direct spin-flip transition of a single quasiparticle trapped in the junction. Finally, we measure a gate- and field-dependent anomalous phase shift of the Andreev spectrum, of magnitude up to ∼0.7π. Our observations demonstrate alternative ways to manipulate Andreev states in a magnetic field and reveal spin-polarized triplet states that carry supercurrent
Mitigation of Quasiparticle Loss in Superconducting Qubits by Phonon Scattering
No full textQuantum error correction will be an essential ingredient in realizing fault-tolerant quantum computing. However, most correction schemes rely on the assumption that errors are sufficiently uncorrelated in space and time. In superconducting qubits, this assumption is drastically violated in the presence of ionizing radiation, which creates bursts of high-energy phonons in the substrate. These phonons can break Cooper pairs in the superconductor and, thus, create quasiparticles over large areas, consequently reducing qubit coherence across the quantum device in a correlated fashion. A potential mitigation technique is to place large volumes of normal or superconducting metal on the device, capable of reducing the phonon energy to below the superconducting gap of the qubits. To investigate the effectiveness of this method, we fabricate a quantum device with four nominally identical nanowire-based transmon qubits. On the device, half of the niobium-titanium-nitride ground plane is replaced with aluminum (Al), which has a significantly lower superconducting gap. We deterministically inject high-energy phonons into the substrate by voltage biasing a galvanically isolated Josephson junction. In the presence of the small-gap material, we find a factor of 2–5 less degradation in the injection-dependent qubit lifetimes and observe that the undesired excited qubit state population is mitigated by a similar factor. We furthermore turn the Al normal with a magnetic field, finding no change in the phonon protection. This suggests that the efficacy of the protection in our device is not limited by the size of the superconducting gap in the Al ground plane. Our results provide a promising foundation for protecting superconducting-qubit processors against correlated errors from ionizing radiation.QRD/Kouwenhoven LabQN/Kouwenhoven LabAndersen La
Effekt der CI-Versorgung im Erwachsenenalter auf das Sprachverstehen und die Lautsprachproduktion bei congenitaler Surditas: ein Fallbericht
No full textDynamical polarization of the fermion parity in a nanowire Josephson junction
No full textJosephson junctions in InAs nanowires proximitized with an Al shell can host
gate-tunable Andreev bound states. Depending on the bound state occupation, the
fermion parity of the junction can be even or odd. Coherent control of Andreev
bound states has recently been achieved within each parity sector, but it is
impeded by incoherent parity switches due to excess quasiparticles in the
superconducting environment. Here, we show that we can polarize the fermion
parity dynamically using microwave pulses by embedding the junction in a
superconducting LC resonator. We demonstrate polarization up to 94% 1%
(89% 1%) for the even (odd) parity as verified by single shot
parity-readout. Finally, we apply this scheme to probe the flux-dependent
transition spectrum of the even or odd parity sector selectively, without any
post-processing or heralding
Singlet-doublet transitions of a quantum dot Josephson junction detected in a transmon circuit
No full textWe realize a hybrid superconductor-semiconductor transmon device in which the
Josephson effect is controlled by a gate-defined quantum dot in an InAs/Al
nanowire. Microwave spectroscopy of the transmon's transition spectrum allows
us to probe the ground state parity of the quantum dot as a function of gate
voltages, external magnetic flux, and magnetic field applied parallel to the
nanowire. The measured parity phase diagram is in agreement with that predicted
by a single-impurity Anderson model with superconducting leads. Through
continuous time monitoring of the circuit we furthermore resolve the
quasiparticle dynamics of the quantum dot Josephson junction across the phase
boundaries. Our results can facilitate the realization of semiconductor-based
qubits and Andreev qubits.Comment: Main text has 14 pages, 7 figures. Supplement has 21 pages, 21
figure
Microwave spectroscopy of interacting Andreev spins
No full textAndreev bound states are fermionic states localized in weak links between
superconductors which can be occupied with spinful quasiparticles. Microwave
experiments using superconducting circuits with InAs/Al nanowire Josephson
junctions have recently enabled probing and coherent manipulation of Andreev
states but have remained limited to zero or small fields. Here we use a
flux-tunable superconducting circuit in external magnetic fields up to 1T to
perform spectroscopy of spin-polarized Andreev states up to ~250 mT, beyond
which the spectrum becomes gapless. We identify singlet and triplet states of
two quasiparticles occupying different Andreev states through their dispersion
in magnetic field. These states are split by exchange interaction and couple
via spin-orbit coupling, analogously to two-electron states in quantum dots. We
also show that the magnetic field allows to drive a direct spin-flip transition
of a single quasiparticle trapped in the junction. Finally, we measure a gate-
and field-dependent anomalous phase shift of the Andreev spectrum, of magnitude
up to approximately . Our observations demonstrate new ways to
manipulate Andreev states in a magnetic field and reveal spin-polarized triplet
states that carry supercurrent
