In contrast to the "standard" Divincenzo paradigm, in which a sequence of one- and two-bit unitary operations evolves a collection of qubits from a known initial state to a state that encodes the output, an adiabatic quantum computer maintains a system of qubits in the ground state of a slowly varying Hamiltonian and is less prone to decoherence.
The initial (unfrustrated) Hamiltonian has a simple ground state, while the final Hamiltonian, which encodes the problem, has a complex ground state that encodes the solution.
In 'standard' quantum computing the solution is encoded in an entangled superposition of states of a multiqubit system, which is fragile with respect to decoherence. This constitutes the main obstacle for a realization of standard quantum computing in the near future.
In adiabatic quantum computing, the solution is encoded in the ground state of the system evolving under an adiabatically slow change of a control parameter, from an easily accessible initial state. The main advantages of adiabatic quantum computing are the following:
- The precise time-dependent control over specific qubits, which is necessary (but hardly realizable) for the standard scheme, is no longer an issue for adiabatic quantum computing.
- Staying in the ground state automatically protects the system against relaxation and dephasing.
- Any standard quantum algorithm can be realized by an adiabatic quantum computer with a local Hamiltonian (which is extremely important for any quantum computing realization).
- Thus, in contrast to standard quantum computing requiring very large number of qubits, some adiabatic quantum computing schemes can be realized with a modest number of physical qubits.
Therefore a solid state-based implementation of an adiabatic quantum computer is feasible.
Research in this area ranges from the principles of adiabatic quantum computing to Josephson-based quantum computing architectures.