Robust entanglement of an asymmetric quantum dot molecular system in a Josephson junction

Abstract

We demonstrate the generation of robust entanglement of a quantum dot molecular system in a voltage-controlled junction. To improve the quantum information characteristics of this system, we propose an applicable protocol which contains the implementation of asymmetric quantum dots as well as the engineering of reservoirs. Quantum dots can provide asymmetric coupling coefficients due to the tunable energy barriers through the gap voltage changes. To engineer the reservoirs, superconducting leads are used to prepare a voltage-biased Josephson junction. The high-controllability properties of this system give the arbitrary magnitude of entanglement by the arrangement of parameters. Significantly, the perfect entanglement can be achieved for an asymmetric structure in response to the increase of bias voltage, and also it continues saturated with the near-unit amount.

Generation of entanglement between quantum dot molecule with the presence of phonon effects in a voltage-controlled junction

“…To quantify entanglement between two qubits, Wootters proposed the measure of concurrence for both pure and mixed states [45,46]. In condensed matter systems, the entanglement of fermions is evaluated by fermionic concurrence [47,48,49,50,51] in analog with Wootter's formula. Therefore, the entanglement between quantum dots including electrons as indistinguishable fermions can be calculated in the formalism of fermionic concurrence that we discussed in the previous paper [51].…”

“…In condensed matter systems, the entanglement of fermions is evaluated by fermionic concurrence [47,48,49,50,51] in analog with Wootter's formula. Therefore, the entanglement between quantum dots including electrons as indistinguishable fermions can be calculated in the formalism of fermionic concurrence that we discussed in the previous paper [51]. Studying the concurrence of quantum dot qubits has attracted considerable attention [52] and particularly, this measure was determined for double quantum dot systems [9,10,51].…”

“…Therefore, the entanglement between quantum dots including electrons as indistinguishable fermions can be calculated in the formalism of fermionic concurrence that we discussed in the previous paper [51]. Studying the concurrence of quantum dot qubits has attracted considerable attention [52] and particularly, this measure was determined for double quantum dot systems [9,10,51]. Here, for our carbon nanotube quantum dot molecule, we define the concurrence as:…”

“…One technique that can be used to reduce the environmental dissipation in the quantum dot system is employing the coupling of quantum dots to reservoirs asymmetrically [9]. Recently, we showed that by using quantum dots with asymmetric coupling coefficients, robust entanglement is achieved for a QDM system in a Josephson junction [51]. Here, to generate entanglement with a remarkable value and preserve it steadily, we define an asymmetric factor in which the coupling coefficients of QDs-metal leads are determined unequal.…”

Integrated programmable controlled phase gate design for quantum information processing

“…Although these results have a limited area of usage, more crucial applications, especially in the fields of cryptography and secure communication, are expected to be achieved in the near future [3]. Besides long-standing efforts of implementing quantum information processing via trapped ions [4,5] or superconductors [6,7], linear optical quantum information processing, which is a relatively new field, demonstrates an outstanding performance. Photons are preferable carriers of quantum information that have little interaction with the environment.…”