Magnetic field compatible circuit quantum electrodynamics with graphene Josephson junctions

Abstract

Circuit quantum electrodynamics has proven to be a powerful tool to probe mesoscopic effects in hybrid systems and is used in several quantum computing (QC) proposals that require a transmon qubit able to operate in strong magnetic fields. To address this we integrate monolayer graphene Josephson junctions into microwave frequency superconducting circuits to create graphene based transmons. Using dispersive microwave spectroscopy we resolve graphene’s characteristic band dispersion and observe coherent electronic interference effects confirming the ballistic nature of our graphene Josephson junctions. We show that the monoatomic thickness of graphene renders the device insensitive to an applied magnetic field, allowing us to perform energy level spectroscopy of the circuit in a parallel magnetic field of 1 T, an order of magnitude higher than previous studies. These results establish graphene based superconducting circuits as a promising platform for QC and the study of mesoscopic quantum effects that appear in strong magnetic fields.

Andreev reflection in ballistic normal metal/graphene/superconductor junctions

“…It proves that these oscillations indeed arise from the FP interference of the Andreev reflected charge carriers. In a Josephson junction, existence of FP interference can be observed in the superconducting state by following the oscillations in the critical current [28][29][30][31][32][33][34][35][36][37][38][39][40][41] or multiple Andreev reflection 33 . However, to the best of our knowledge, it is the first time that the effect of vi FP resonances have been observed in superconducting state in NGS junctions.…”

“…The development of van der Waals heterostructures designed from two-dimensional materials [23][24][25] in addition to the recent progresses in sample fabrication 26,27 , dramatically improved both charge carrier mobility and contact transparency in graphene-based electrical devices. As a consequence, the study of proximity induced superconductivity regained interest with the possibilities to measure large supercurrents and ballistic interferences [28][29][30][31][32][33][34][35][36][37][38][39][40][41] . However, most of the studies related to Andreev processes in this system usually consist of probing the dissipationless current and multiple Andreev reflection in graphene connected to two superconducting contacts, while Andreev bound states in graphene have been detected by tunnelling spectroscopy experiments 42 .…”

Josephson penetration depth in coplanar junctions based on 2D materials

“…These represent limiting cases: in Geometry A, the width of the superconducting electrodes is much larger than the width of the 2D material; while in Geometry B, the width of the superconducting electrodes is the same as that of the 2D material. Most of the experiments in the literature adopted Geometry A [1,3,6,8,9,12,14,17,18,26,27], while a few of them are better described by Geometry B (or somewhere between Geometry A and Geometry B [2,4,10,11,13,15,16,19,20]). When the superconducting electrodes are thicker than the London penetration depth , the supercurrent tends to flow in a narrow region within ~ from the edge of the superconducting electrodes as shown.…”

Anomalous phase dynamics of driven graphene Josephson junctions

“…Through comparison to simulations, the time scale is shown to depend sensitively on the CPR of the junction, becoming large for skewed CPRs like that predicted for weak links materials possessing a Dirac (linear) energy dispersion. These results should inform future experiments using RF radiation to probe exotic materials in JJs [7][8][9] and devices that exploit JJs in RF environments [25,26].…”