Quantum Current Flow

Adrien Reingruber, Kitinan Pongsangangan, Fakher F. Assaad +1 more

The emergence of hydrodynamic behavior in electronic flow within clean, particle-hole-symmetric systems at half filling is a nontrivial problem. Navier-Stokes (NS) equations describe the momentum flow, while experimental measurements typically capture the current flow profiles. However, in particle-hole-symmetric systems, electric current and momentum flow are entirely decoupled, because electrons and holes move in opposite directions with equal distribution functions. This makes it challenging to link NS equations to observed flow patterns. In this Letter, we demonstrate that the hydrodynamic behavior of the charge current at half filling can emerge despite the absence of momentum flow. By combining Boltzmann transport theory with numerically exact quantum Monte Carlo simulations of clean graphene samples, we show that NS-type equations can be derived directly for the charge current, eliminating the need for any additional mechanism coupling the velocity field and charge current in explaining the experimentally observed hydrodynamic flow profiles in graphene at half filling. We show that a new transport quantity-the current diffusion coefficient-replaces viscosity and expect this description to be valid for any particle-hole-symmetric system. Our results provide new insights into the interpretation of experimental data and demonstrate how quantum Monte Carlo calculations can serve as an alternative to experiments in transport measurements to verify the kinetic theory results.

Shaowen Chen, Seunghyun Park, Uri Vool +8 more

Josephson junctions enable dissipation-less electrical current through metals and insulators below a critical current. Despite being central to quantum technology based on superconducting quantum bits and fundamental research into self-conjugate quasiparticles, the spatial distribution of super current flow at the junction and its predicted evolution with current bias and external magnetic field remain experimentally elusive. Revealing the hidden current flow, featureless in electrical resistance, helps understanding unconventional phenomena such as the nonreciprocal critical current, i.e., Josephson diode effect. Here we introduce a platform to visualize super current flow at the nanoscale. Utilizing a scanning magnetometer based on nitrogen vacancy centers in diamond, we uncover competing ground states electrically switchable within the zero-resistance regime. The competition results from the superconducting phase re-configuration induced by the Josephson current and kinetic inductance of thin-film superconductors. We further identify a new mechanism for the Josephson diode effect involving the Josephson current-induced phase. The nanoscale super current flow emerges as a new experimental observable for elucidating unconventional superconductivity, and optimizing quantum computation and energy-efficient devices. Diract imaging of supercurrent flow at a Josephson junction has been inaccessible in experiment. Here, using nanoscale magnetometry, the authors find large kinetic inductance of thin film superconductors can lead to competing Josephson vortex states hidden below the critical current, and also provide a new route towards the Josephson diode effect.

Jincheng Zhang

This paper introduces the concept of Entanglement Topological Flow (ETF), a novel framework proposing that entanglement is not a static correlation but rather a dynamic, flowing quantity. We posit that entanglement can be described mathematically as a current-like flow, denoted by `J_E`, analogous to electric current. This framework offers a new perspective on understanding entanglement, potentially bridging the gap between quantum information theory and condensed matter physics. We outline the theoretical foundations of ETF, focusing on entanglement dynamics and its implications for multi-qubit networks. The proposed ETF model holds significant promise for advancing our understanding of entanglement and could potentially lead to breakthroughs in quantum technologies, warranting consideration for Nobel Prize recognition. ---