Entanglement of two superconducting charge qubits with the Glauber–Lachs state

Abstract

We investigate the entanglement properties of two superconducting charge qubits that share a large Josephson junction where the field is assumed to be prepared initially in a Glauber-Lachs state. We explore the increasing effect of the chaotic field due to the thermal photons on the entanglement properties of these two superconducting charge qubits. We show that the entanglement of the qubits is very sensitive to thermal photons. The chaotic effect of the field has a reducing effect on the entanglement degree of the qubits. Also, we draw a parallelism between the Glauber-Lachs state and the random telegraph noise by means of the entanglement.

Entropy squeezing of a Jaynes–Cummings atom with the Glauber–Lachs state

“…Some authors have studied the Glauber-Lachs state in the realm of the JCM and revealed some dynamical properties of atom-field interactions [5][6][7][8]. In [8,9], we studied the entanglement dynamics in the qubit(s)-field interaction with the Glauber-Lachs state and showed that the thermal photons in the Glauber-Lachs state may be considered as the injection of a quasi-intrinsic decoherence mechanism into the atom-coherent field interaction, since these photons produce disorder or noise. In this paper, we explore another dynamical quantity in the qubit-field interaction with the Glauber-Lachs state.…”

“…We need the atomic density matrix (ρ a (t)), which is obtained by tracing out ρ(t) in equation ( 8) over the degree of freedom of the field |n . In this case, ρ a (t) takes the form ρ a (t)=ρ ee (t)|e e|+ρ eg (t)|e g|+ρ ge (t)|g e|+ρ gg (t)|g g|, (9) where the time-dependent coefficients are given by…”

“…An alternative definition in [10] is as follows: the authors defined an entropy squeezing factor E(S k ), The fluctuations in the component S k (k = x, y) are squeezed if E(S k ) < 0. In order to compute the expressions in equation ( 17), we need the probability distributions (P i (S k )), which are obtained from the atomic density matrix in equation (9). In this case, we obtain the following expressions:…”

“…But in the S y component, increasing the number of thermal photons gradually destroys the entropy squeezing as time progresses. This is because, increasing the number of thermal photons in the coherent field intensifies the chaotic nature of the interaction and accordingly produces a quasi-intrinsic decoherence mechanism in the interaction [8,9]. So, entropy squeezing, which is a quantum property of the system, vanishes during the time evolution of the system.…”

Entanglement of two superconducting charge qubits with transient effects

“…In [8,9] the authors also gave the recent results on quantum correlations in such quantum circuits. In our a previous work [10], we investigated the entanglement of two superconducting charge qubits sharing a large Josephson junction where the field is in a Glauber-Lachs state. We showed that the entanglement of the qubits is a monotonic function of the value of the thermal photons.…”