getConcurrence

returns the concurrence between two qbits, using Wooters formula (Entanglement of Formation of an Arbitrary State of Two Qubits)

Contents

Syntax

getConcurrence()

Description

getConcurrence() returns the concurrence, which is a measure for entanglement between two qbits. This command can be used in the context of an arbitrary system. However, if the system contains more than 2 qbits all other qibts have to be traced out first using the traceOut(name) command.

Example of two qbits which are coupled via a cavity

clear; close all;
s = System;
a = Nlevel(1);
s.addEntity(a,'qbit');
s.addEntity(Qoscillator(3,1),'cavity');
s.addEntity(Nlevel(1),'qbit2');
s.addCoupling('qbit','cavity',0.05);
s.addCoupling('cavity','qbit2',0.05);
s.addDissipation('qbit',200);
s.addExternalField(Gausspulse(0.04,100,30,1),'qbit');
s.setTmax(400);
s.setTimestep(0.1);
s.simulate;
s.traceOut('cavity')
h =plot(s.time,s.getConcurrence);
xlabel('Time in au');
ylabel('Concurrence')

The above graphs show the concurrence between the two indirectly coupled qbits. This concurrence is calculated using the reduced density matrix reduced_rho_hist.