Superconducting transport in single and parallel double InAs quantum dot Josephson junctions with Nb-based superconducting electrodes

Abstract

We report conductance and supercurrent measurements for InAs single and parallel double quantum dot Josephson junctions contacted with Nb or NbTiN superconducting electrodes. Large superconducting gap energy, high critical field and large switching current are observed, all reflecting the features of Nb-based electrodes. For the parallel double dots we observe an enhanced supercurrent when both dots are on resonance, which may reflect split Cooper pair tunneling. TEXTInherently low-dimensional semiconductors, such as nanowires, nanotubes, and self-assembled quantum dots, are attractive research materials, because their natural geometries are suited to study anisotropic quantum effects, and they are easily combined with superconductors or ferromagnets to investigate hybrid quantum effects. In particular, by directly contacting self-assembled quantum dots (SAQDs) with normal metal electrodes, gate-tunable electronic properties of confined electrons have been revealed, such as anisotropic and tunable spin-orbit interaction 1,2 and g-factor 2,3 , and tunable Kondo-effect 4,5 . For hybrid devices contacted with superconducting electrodes various kinds of proximity induced quantum transport have been revealed, including non-dissipative , spectroscopy of Andreev energy levels 7,8 , and competition between superconducting proximity effect and Kondo screening 9,10 . In most of these studies aluminum (Al) is used for the superconducting contacts primarily because it is an easy material for making small but robust superconducting junctions with well-established nano-fabrication techniques. Though experiments on QD Josephson junctions (QDJJs) with Al electrodes have been very successful to date, the parameter space is restricted to low magnetic field and low temperature and in most devices the superconducting energy gap maybe small compared with other energy scales. A superconductor with a large superconducting gap and a high critical field would extend the parameter space that can be studied with QDJJs and open new possibilities to study devices in high magnetic fields. One area in which high T c leads may be of benefit is the study of Cooper-pair beam splitting with two quantum dots parallel coupled to a superconductor, which provides a source of non-local entangled electron pairs for quantum information processing and quantum electron optics. Although Cooper-pair splitting is confirmed in several studies [11][12][13][14] with InAs nanowire or carbon nanotube devices, to prove the maintenance of the spin-singlet correlation after pairsplitting remains challenging. We have recently observed increased switching current for parallel double quantum dot Josephson junctions (DQDJJs) with Al electrodes when both dots are on resonance, indicating split but correlated Cooper pair tunneling through the two dots 15 . To further study the spin correlation in the split tunneling of paired electrons it is proposed to detect the phase factor in two path interference [16][17][18] , for which parallel double [19][20][21][22][23]...

Phase-dependent heat and charge transport through superconductor–quantum dot hybrids

“…[42] and [43] for recent reviews on experiments and theory, respectively. In particular, there are investigations of the Josephson effect through quantum dots [44][45][46][47][48][49], multiple Andreev reflections [50][51][52][53][54][55], the interplay between superconducting correlations and the Kondo effect [56][57][58][59][60][61], the generation of unconventional superconducting correlations in quantum dots [62][63][64][65], Cooper pair splitting [66][67][68][69][70][71] and the generation of Majorana fermions [72][73][74][75]. Thermoelectric effects in superconductor-quantum dot hybrids have been studied in the absence of Coulomb interactions [76].…”

Gate tunable parallel double quantum dots in InAs double-nanowire devices

“…In this study we repot on fabrication and characterization of InAs DNW junctions, where a quantum dot is formed in each NW, and evaluated the gate performances. The DNW devices are useful for making multiple spin qubits and topological circuits of non-local entangled electrons [15][16][17][18][19] or parafermions as well as majorana fermions 20 . We develop a fabrication technique for selectively placing DNW onto previously fabricated gate arrays and selectively contacting the two NWs.…”

MBE growth of Al/InAs and Nb/InAs superconducting hybrid nanowire structures

“…For instance, the coupling of gate-defined qubits at the nanowire ends via a superconductor has been proposed 2 , but also quantum network structures 5 . Further, gateable nanowire-based Josephson junctions [6][7][8] are in the focus of ongoing research. SC/InAs systems have been predicted to provide the optimal environment for proximity-induced p-wave superconductivity, leading in presence of an external magnetic field to spinless quasiparticles in form of triplet state Cooper pairs within the semiconductor 4,9 .…”