Loss–DiVincenzo quantum computer
Loss–DiVincenzo quantum computer
The Loss–DiVincenzo quantum computer (or spin-qubit quantum computer) is a scalable semiconductor-based quantum computer proposed by Daniel Loss and David P. DiVincenzo in 1997.[1] The proposal was to use as qubits the intrinsic spin-1/2 degree of freedom of individual electrons confined to quantum dots. This was done in a way that fulfilled DiVincenzo Criteria for a scalable quantum computer,[2] namely:
identification of well-defined qubits;
reliable state preparation;
low decoherence;
accurate quantum gate operations and
strong quantum measurements.
A candidate for such a quantum computer is a lateral quantum dot system.
Implementation of the two-qubit gate
The Loss–DiVincenzo quantum computer operates, basically, using inter-dot gate voltage for implementing Swap (computer science) operations and local magnetic fields (or any other local spin manipulation) for implementing the Controlled NOT gate (CNOT gate).
The Swap operation is achieved by applying a pulsed inter-dot gate voltage, so the exchange constant in the Heisenberg Hamiltonian becomes time-dependent:
This description is only valid if:
the level spacing in the quantum-dot is much greater than ;
the pulse time scale is greater than , so there is no time for transitions to higher orbital levels to happen and
the decoherence time is longer than .
From the pulsed Hamiltonian follows the time evolution operator
