Quantum Interferometry for Different Energy Landscapes in a Tuneable Josephson Junction Circuit

This paper presents a simple Josephson-junction circuit with two parameters (inductance and capacitance) which can be tuned to represent different energy landscapes with different physical properties. By tuning this quantum circuit through external accessible elements we can move from two to three and more energy levels depending on the parameter setting. The inductance, the capacitance as well as the external voltage (driving terms) condition the number of relevant energy levels as well as the model to be used. We show that the quantized circuit represents a multi-state system with tunneling induced by the Landau-Zener and Landau-Zener-Stückelberg transition. The special cases of single crossing and multi-crossing models are thoroughly studied and the transition probability is obtained in each case. It is proven that, the crossing time as well as the relaxation time affect drastically the transition probability;the system mimics a single passage for short relaxation and a multiple passage problem for large relaxation. The nonlinearity of energy levels modifies the transition probability and the derived adiabatic parameters help to redefine the Landau-Zener probability. The observed constructive and destructive interferences are parametrically conditioned by the initial condition set by the inductive branch. Moreover, the total population transfers as well as the complete blockage of the system are obtained in a permissible range of parameters only by changing the values of the inductance. Therefore, the system models a controllable level-crossing where the additional branches (inductive and capacitive) help in designing the number of states, the type of interferometry as well as the control of states occupation.

Nonlinear quantum interferometry with Bose condensed atoms

In quantum interferometry, it is vital to control and utilize nonlinear interactions for the achievement of high-precision measurements. Due to their long coherence time and high controllability, ultracold atoms including Bose condensed atoms have been widely used for quantum interferometry. Here, we review recent progress in theoretical studies of quantum interferometry with Bose condensed atoms. In particular, we focus on nonlinear phenomena induced by atom-atom interactions, and how to control and utilize these nonlinear phenomena. With a mean-field description, due to atom-atom interactions, matter-wave solitons appear in the interference patterns, and macroscopic quantum self-trapping exists in Bose-Josephson junctions. With a many-body description, atom-atom in- teractions can generate non-classical entanglement, which can be utilized to achieve high-precision measurements beyond the standard quantum limit.

Quantum vector DC magnetometry via selective phase accumulation

Precision measurement of magnetic fields is a crucial issue in both fundamental scientific research and practical sensing technology.The sensitive detection of a vector magnetic field poses a significant challenge in quantum magnetometry,particularly in estimating a vector DC magnetic field with high precision.Here,we propose a comprehensive protocol for quantum vector DC magnetometry,utilizing selective phase accumulation in both non-entangled and entangled quantum probes.Building upon the principles of Ramsey interferometry,our protocol enables the selective accumulation of phase for a specific magnetic field component by incorporating a meticulously designed pulse sequence.In the individual measurement scheme,we employ three individual quantum interferometries to independently estimate each of the three magnetic field components.Alternatively,in the simultaneous measurement scheme,the application of a pulse sequence along different directions enables the simultaneous estimation of all three magnetic field components using only one quantum interferometry.Notably,by employing an entangled state(such as the Greenberger-Horne-Zeilinger state)as the input state,the measurement precisions of all three components may reach the Heisenberg limit.This study not only establishes a general protocol for measuring vector magnetic fields using quantum probes,but also presents a viable pathway for achieving entanglement-enhanced multi-parameter estimation.