Graphene Photonics I/Q Modulator for Advanced Modulation Formats.

Starting from its classical domain of long distance links, optical communication is conquering new application areas down to chip-to-chip interconnections in response to the ever-increasing demand for higher bandwidth. The use of coherent modulation formats, typically employed in long-haul systems, is now debated to be extended to short links to increase the bandwidth density. Next-generation transceivers are targeting high bandwidth, high energy efficiency, compact footprint, and low cost. Integrated photonics is the only technology to reach this goal, and silicon photonics is expected to play the leading actor. However, silicon modulators have some limits, in terms of bandwidth and footprint. Graphene is an ideal material to be integrated with silicon photonics to meet the requirements of next generation transceivers. This material provides optimal properties: high mobility, fast carrier dynamics and ultrabroadband optical properties. Graphene photonics for direct detection systems based on binary modulation formats have been demonstrated so far, including electro-absorption modulators, phase modulators, and photodetectors. However, coherent modulation for increased data-rates has not yet been reported for graphene photonics yet. In this work, we present the first graphene photonics I/Q modulator based on four graphene on silicon electro-absorption modulators for advanced modulation formats and demonstrate quadrature phase shift keying (QPSK) modulation up to 40 Gb/s.

Preliminary demonstration of a persistent Josephson phase-slip memory cell with topological protection.

Superconducting computing promises enhanced computational power in both classical and quantum approaches. Yet, scalable and fast superconducting memories are not implemented. Here, we propose a fully superconducting memory cell based on the hysteretic phase-slip transition existing in long aluminum nanowire Josephson junctions. Embraced by a superconducting ring, the memory cell codifies the logic state in the direction of the circulating persistent current, as commonly defined in flux-based superconducting memories. But, unlike the latter, the hysteresis here is a consequence of the phase-slip occurring in the long weak link and associated to the topological transition of its superconducting gap. This disentangles our memory scheme from the large-inductance constraint, thus enabling its miniaturization. Moreover, the strong activation energy for phase-slip nucleation provides a robust topological protection against stochastic phase-slips and magnetic-flux noise. These properties make the Josephson phase-slip memory a promising solution for advanced superconducting classical logic architectures or flux qubits.

Gate Control of the Current-Flux Relation of a Josephson Quantum Interferometer Based on Proximitized Metallic Nanojuntions.

We demonstrate an Al superconducting quantum interference device in which the Josephson junctions are implemented through gate-controlled proximity Cu mesoscopic weak links. This specific kind of metallic weak links behaves analogously to genuine superconducting metals in terms of the response to electrostatic gating and provides a good performance in terms of current-modulation visibility. We show that through the application of a static gate voltage we can modify the interferometer current-flux relation in a fashion that seems compatible with the introduction of π-channels within the gated weak link. Our results suggest that the microscopic mechanism at the origin of the suppression of the switching current in the interferometer is apparently phase coherent, resulting in an overall damping of the superconducting phase rigidity. We finally tackle the performance of the interferometer in terms of responsivity to magnetic flux variations in the dissipative regime and discuss the practical relevance of gated proximity-based all-metallic SQUIDs for magnetometry at the nanoscale.

A Josephson phase battery.

A classical battery converts chemical energy into a persistent voltage bias that can power electronic circuits. Similarly, a phase battery is a quantum device that provides a persistent phase bias to the wave function of a quantum circuit. It represents a key element for quantum technologies based on phase coherence. Here we demonstrate a phase battery in a hybrid superconducting circuit. It consists of an n-doped InAs nanowire with unpaired-spin surface states, that is proximitized by Al superconducting leads. We find that the ferromagnetic polarization of the unpaired-spin states is efficiently converted into a persistent phase bias φ0 across the wire, leading to the anomalous Josephson effect1,2. We apply an external in-plane magnetic field and, thereby, achieve continuous tuning of φ0. Hence, we can charge and discharge the quantum phase battery. The observed symmetries of the anomalous Josephson effect in the vectorial magnetic field are in agreement with our theoretical model. Our results demonstrate how the combined action of spin-orbit coupling and exchange interaction induces a strong coupling between charge, spin and superconducting phase, able to break the phase rigidity of the system.

High operating temperature in V-based superconducting quantum interference proximity transistors.

Here we report the fabrication and characterization of fully superconducting quantum interference proximity transistors (SQUIPTs) based on the implementation of vanadium (V) in the superconducting loop. At low temperature, the devices show high flux-to-voltage (up to 0.52 mV/Φ0) and flux-to-current (above 12 nA/Φ0) transfer functions, with the best estimated flux sensitivity ~ 2.6 µΦ0/(Hz)1/2 reached under fixed voltage bias, where Φ0 is the flux quantum. The interferometers operate up to T bath [Formula: see text] 2 K, with an improvement of 70% of the maximal operating temperature with respect to early SQUIPTs design. The main features of the V-based SQUIPT are described within a simplified theoretical model. Our results open the way to the realization of SQUIPTs that take advantage of the use of higher-gap superconductors for ultra-sensitive nanoscale applications that operate at temperatures well above 1 K.