arXiv subjects

Cliff Sun

Publications and source records attributed to Cliff Sun.

4 recordsLinked to original sources

arXiv2026

Symmetry of the critical current function in superconducting nanodevices

We study a variety of nano-scale superconducting devices containing more than one weak link. Even in devices with multiple weak links the IB symmetry is usually obeyed, which means that if we reverse both the bias current direction and the magnetic field direction at the same time, the superconducting response, namely the critical current, remains unchanged. We also provide a detailed analysis of the situations in which such symmetry is violated.

cond-mat.supr-con↗

arXiv2026

A Dayem Loop Qubit Based on Interfering Superconducting Nanowires

We propose a qubit design based on two parallel superconducting nanowires (i.e., a "Dayem loop qubit"). The inclusion of two nanowires instead of one leads to the Little-Parks effect, which provides an oscillator behavior for the qubit frequency as well as anharmonicity. Our key result is that even if the nanowires have an increasingly linear CPR at low supercurrents, the quantum interference between two condensates, induced by a magnetic field, leads to a restoration of cubic nonlinearity, which is predicted to be sufficient to create a functional transmon qubit based on thin superconducting wires. We consider both generic (cubic) current-phase relationships (CPR) as well as more realistic microscopic CPR, having higher-order nonlinearities. For higher-order CPRs, we propose a simple power-law phenomenological approximation valid at very low temperatures, at which superconducting qubits normally operate.

cond-mat.supr-con↗

arXiv2025

Perfect Superconducting Diode and Supercurrent Range Controller

Diodes have a nonreciprocal voltage versus current relationship, produced by breaking the space and time reversal symmetry. However, developing high-end superconducting computers requires a superconducting analogue of the traditional semiconductor diode. Such a superconducting diode exhibits non-reciprocity, or a high asymmetry in its critical currents. We present a model of a perfect superconducting diode based on a superconducting quantum interference device made with multiple superconducting nanowires. The diode predicted by our model has a large positive critical current, while the negative critical current can be exactly zero. This 100\% diode efficiency ($\eta = 1$) remains stable against small changes of the magnetic field. Another important result is that under certain and quite broad conditions such devices can act as supercurrent range controllers. In such device a supercurrent can flow with zero voltage applied, but only if the supercurrent is contained in some narrow, adjustable range, which excludes zero current.

cond-mat.supr-con↗

arXiv2025

Multiple-Nanowire Superconducting Quantum Interference Devices: Critical Currents, Symmetries, and Vorticity Stability Regions

An ordinary superconducting quantum interference device (SQUID) contains two weak links connected in parallel. We model a multiple-wire SQUID (MW-SQUID), generalized in two ways. First, the number of weak links, which are provided by parallel superconducting nanowires, is larger than two. Second, the current-phase relationship of each nanowire is assumed linear, which is typical for a homogeneous superconducting thin wire. For such MW-SQUIDs, our model predicts that the critical current ($I_c$) is a multi-valued function of the magnetic field. We also calculate vorticity stability regions (VSR), i.e., regions in the current-magnetic field plane in which, for a given distribution of vortices, the currents in all wires are below their critical values, so the vortices do not move between the cells. The VSRs have rhombic shapes in the case of two-wire SQUIDS and have more complicated shapes in the case of many nanowires. We present a classification of such VSRs and determine conditions under which VSR is disjoint, leading to 100\% supercurrent modulation and quantum phase transitions. According to the model, the maximum critical current curves obey $IB$ symmetry, while each VSR obeys $IBV$ symmetry. The model predicts conditions at which MW-SQUID exhibits a perfect diode effect in which the critical current of one polarity is zero while it is not zero for the opposite polarity of the bias current. We also provide a classification of the stability regions produced by (1) completely symmetric, (2) phase disordered, (3) position disordered, (4) critical current disordered, and (5) completely disordered multi-wire SQUIDs.

cond-mat.supr-con↗