Quantum breathers in capacitively coupled Josephson junctions: Correlations, number conservation, and entanglement

Abstract

We consider the classical and quantum dynamics of excitations in a system of two capacitively coupled Josephson junctions. In the classical case the equations of motion admit discrete breather solutions, which are time periodic and localized predominantly on one of the junctions. In the quantum case breather states are found in the central part of the energy spectrum of the confined nonescaping states of the system. We perform a systematic analysis of their tunneling frequency, site correlations, fluctuations of the number of quanta, and entanglement. Quantum breather states show strong site correlation of quanta and are characterized by a strong excitation of quanta on one junction which perform slow coherent tunneling motion from one junction to the other. They suppress fluctuations of the total number of excited quanta. Quantum breather states are the least entangled states among the group of eigenstates in the same range of the energy spectrum. We describe how quantum breather excitations could be experimentally observed by employing the already developed techniques for quantum information processing using Josephson junctions.

Discrete breathers — Advances in theory and applications

“…Recent studies of Pinto et al [317,316] deal with quantum breather excitations in two capacitively coupled Josephson junctions. Such systems are currently under experimental investigation, being candidates for quantum information processing, and show remarkably long coherence times up to 100 ns for few quanta excitations.…”

Microwave irradiation on a-axis oriented Y123/Pr123 two-stacked Josephson junctions device

“…With increased energy these cooper pairs cross one junction barrier (Pr123) which reflect in the IeV characteristics as the voltage steps. With increase in the power of external microwave the energy level of the Cooper pairs also increase and results passing more number of junction barrier [20]. As increasing the number of junctions barriers these value of voltage step also increases.…”

Controlling quantum breathers in Heisenberg ferromagnetic spin chains via an oblique magnetic field

“…Therefore, it is worth investigating quantum version of discrete breathers, which are generally called quantum breathers. In quantum mechanics, quantum breathers appear as nearly degenerate many‐quanta bound states, taking a very long time to tunnel from one lattice site to another .…”