Charge-4e supercurrent in a two-dimensional InAs-Al superconductor-semiconductor heterostructure

Abstract

Superconducting qubits with intrinsic noise protection offer a promising approach to improve the coherence of quantum information. Crucial to such protected qubits is the encoding of the logical quantum states into wavefunctions with disjoint support. Such encoding can be achieved by a Josephson element with an unusual charge-4e supercurrent emerging from the coherent transfer of pairs of Cooper-pairs. In this work, we demonstrate the controlled conversion of a conventional charge-2e dominated to a charge-4e dominated supercurrent in a superconducting quantum interference device (SQUID) consisting of gate-tunable planar Josephson junctions. We investigate the ac Josephson effect of the SQUID and measure a dominant photon emission at twice the fundamental Josephson frequency together with a doubling of the number of Shapiro steps, both consistent with the appearance of charge-4e supercurrent. Our results present a step towards protected superconducting qubits based on superconductor-semiconductor hybrid materials.

Flux-Tunable Josephson Diode Effect in a Hybrid Four-Terminal Josephson Junction

“…29,30 Such CPRs, containing contributions from higher harmonics than the conventional 2π-periodic component, are routinely attained in high-quality superconductor−semiconductor planar materials, 31−33 where hybrid JJs host Andreev bound states (ABSs) characterized by high transmission. Key ingredients for the JDE to occur in this system are the different harmonic content between the two JJs and a magnetic flux threading the SQUID loop, 29 (2D) electron 34,35 and hole 36 systems, obtaining large diode efficiencies at equilibrium up to approximately 30%. Multiterminal JJs are emerging as a promising platform to investigate supercurrent nonreciprocities.…”

“…Since its observation in superconducting multilayers, the SDE has been the subject of thorough experimental and theoretical investigation, both in junction-free thin films − and JJs based on semiconductors with spin–orbit coupling, − finite-momentum superconductors, − or multilayered materials, realizing sizable asymmetries even without external magnetic fields. − An alternative platform proposed to achieve the SDE in Josephson deviceswhere it is usually referred to as the Josephson diode effect (JDE)relies on a supercurrent interferometer, where two JJs with nonsinusoidal current–phase relations (CPRs) are combined in a SQUID. , Such CPRs, containing contributions from higher harmonics than the conventional 2π-periodic component, are routinely attained in high-quality superconductor–semiconductor planar materials, − where hybrid JJs host Andreev bound states (ABSs) characterized by high transmission. Key ingredients for the JDE to occur in this system are the different harmonic content between the two JJs and a magnetic flux threading the SQUID loop, as recently demonstrated in two-dimensional (2D) electron , and hole systems, obtaining large diode efficiencies at equilibrium up to approximately 30%.…”

Flux-tunable regimes and supersymmetry in twisted cuprate heterostructures

“…21 Over the years, significant research efforts focused on understanding and characterizing dielectric properties of materials [22][23][24] to reduce capacitive losses as well as on the development of alternative qubit designs exploiting external magnetic fluxes or gates to drive the qubit to regimes with vanishing sensitivity to this kind of noise. Notable examples are the rhombus chain, [25][26][27][28] the 0-p, [29][30][31] the bifluxon, 32 the blochnium, 33 the KITE, 34,35 and semiconductor-superconductor [36][37][38][39] qubits, which can be employed also for hybrid topological protection schemes. 40,41 A crucial difference between these qubits and the flowermon is that in the latter, protection originates from the d-wave nature of the order parameter, while in the former, it is achieved through circuit engineering.…”