arXiv:1808.05837 · Physical Review Letters

Supercurrent in a Double Quantum Dot

Juan Carlos Estrada Saldaña, Alexandros Vekris, Gorm O. Steffensen, Rok Žitko, Peter Krogstrup, Jens Paaske, Kasper Grove‐Rasmussen, Jesper Nygård

Published Dec 20, 2018• 63 citations

arXiv HTML PDF

Abstract

We demonstrate the Josephson effect in a serial double quantum dot defined in a nanowire with epitaxial superconducting leads. The supercurrent stability diagram adopts a honeycomb pattern. We observe sharp discontinuities in the magnitude of the critical current, I_{c}, as a function of dot occupation, related to doublet to singlet ground state transitions. Detuning of the energy levels offers a tuning knob for I_{c}, which attains a maximum at zero detuning. The consistency between experiment and theory indicates that our device is a faithful realization of the two-impurity Anderson model.

DOI: 10.1103/physrevlett.121.257701

Related papers

Triplet-blockaded Josephson supercurrent in double quantum dots

Daniël Bouman, Ruben J. J. van Gulik, Gorm O. Steffensen +7 more

Serial double quantum dots created in semiconductor nanostructures provide a versatile platform for investigating two-electron spin quantum states, which can be tuned by electrostatic gating and an external magnetic field. In this Rapid Communication, we directly measure the supercurrent reversal between adjacent charge states of an InAs nanowire double quantum dot with superconducting leads, in good agreement with theoretical models. In the even charge parity sector, we observe a supercurrent blockade with increasing magnetic field, corresponding to the spin singlet to triplet transition. Our results demonstrate a direct spin to supercurrent conversion, the superconducting equivalent of the Pauli spin blockade. This effect can be exploited in hybrid quantum architectures coupling the quantum states of spin systems and superconducting circuits.

arXiv:2008.04375Physical review. B./Physical review. BDec 21, 202033 citations

Magnetic flux controlled current phase relationship in double quantum dot Josephson junction

Yiyan Wang, Cong Li, Bing Dong

Abstract In this study, we investigate the quantum phase transition in a Josephson junction consisting of parallel-connected quantum dots (QDs) with a magnetic flux φ B threading the central region. Employing the surrogate model approach, we discretize the superconducting (SC) electrode into three discrete energy levels, which enables direct diagonalization of the Hamiltonian to determine the system’s ground state. Our calculations demonstrate that when Coulomb interaction is present in only one QD, the system exhibits a phase transition between singlet and doublet states. The magnetic flux exerts a minor influence on the singlet state while substantially affecting the doublet state. When both QDs possess Coulomb interactions, the system undergoes two successive phase transitions as the SC phase difference increases: the ground state evolves from a doublet to a singlet and subsequently to a triplet state at ϕ = π . Enhancement of the magnetic flux suppresses the doublet and triplet phases, ultimately stabilizing the singlet state. Within this regime, increasing the Coulomb interaction strength U does not trigger a singlet-triplet transition; rather, it induces a transition between upper and lower singlet states, resulting in a pronounced peak in the critical current as U increases. Finally, we explore the scenario where the tunneling self-energy Γ between the QDs and SCs exceeds the SC pairing potential Δ. In this case, doublet states prevail, and the system manifests a phase transition exclusively between doublet and triplet states when ϕ B = 0 . Upon application of a magnetic flux, all three states converge, giving rise to a triple point in the ( φ , φ B ) parameter space.

arXiv:2509.17517New Journal of PhysicsMar 31, 20260 citations

Josephson Junction π−0 Transition Induced by Orbital Hybridization in a Double Quantum Dot

Rousan Debbarma, Athanasios Tsintzis, Markus Aspegren +5 more

In this Letter, we manipulate the phase shift of a Josephson junction using a parallel double quantum dot (QD). By employing a superconducting quantum interference device, we determine how orbital hybridization and detuning affect the current-phase relation in the Coulomb blockade regime. For weak hybridization between the QDs, we find π junction characteristics if at least one QD has an unpaired electron. Notably the critical current is higher when both QDs have an odd electron occupation. By increasing the inter-QD hybridization the critical current is reduced, until eventually a π-0 transition occurs. A similar transition appears when detuning the QD levels at finite hybridization. Based on a zero-bandwidth model, we argue that both cases of phase-shift transitions can be understood considering an increased weight of states with a double occupancy in the ground state and with the Cooper pair transport dominated by local Andreev reflection.

arXiv:2311.11867Physical Review LettersDec 21, 20238 citations

Singlet-Doublet Transitions of a Quantum Dot Josephson Junction Detected in a Transmon Circuit

Arno Bargerbos, Marta Pita‐Vidal, Rok Žitko +10 more

We 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-π qubits and Andreev qubits.

arXiv:2202.12754PRX QuantumJul 21, 202276 citations

Critical Current 0−π Transition in Designed Josephson Quantum Dot Junctions

H. I. Jørgensen, Tomáš Novotný, Kasper Grove‐Rasmussen +2 more

We report on quantum dot based Josephson junctions designed specifically for measuring the supercurrent. From high-accuracy fitting of the current-voltage characteristics, we determine the full magnitude of the supercurrent (critical current). Strong gate modulation of the critical current is observed through several consecutive Coulomb blockade oscillations. The critical current crosses zero close to, but not at, resonance due to the so-called 0-pi transition in agreement with a simple theoretical model.

arXiv:0707.3613Nano LettersJul 18, 2007161 citations

Two Anderson impurities coupled through a superconducting island: charge stability diagrams and double impurity qubit

Filip K. Malinowski

We present a model of two Anderson impurities coupled to and through a superconducting island. The model parametrizes the strength of the coupling between impurity sites, allowing it to represent a variable distance between the impurities. We systematically explore the effect of the model parameters in the subspaces with total even and odd occupancy, identifying unique features of the charge stability diagrams that distinguish the two parities. For total odd electron parity, we identify a device tuning, in which the splitting between the two lowest energy states is highly insensitive to changes of the chemical potentials. We investigate the degree to which a qubit based on such two states is tunable and discuss an optimal choice of parameters to maximize inhomogeneous dephasing time. Finally, we point out that the proposed qubit lacks a transition dipole moment, and outline some of the consequences on viable driving and readout mechanisms. The prototype qubits could be realized with the existing capabilities of coupling quantum dots to hard-gapped superconductors.

arXiv:2303.14410Mar 25, 20231 citation