In the circuit QED architecture, the large degree of control over
the designed system parameters and their tunability during
experiments are extremely attractive for quantum computation
(A. Blais et al.).
This system provides an ideal setting to reduce
the coupling of the quantum twolevel system, i.e. the qubit, to
the environment in order to reduce decoherence, while at the same
time allowing for the strong and controlled coupling to a single
degree of freedom, i.e. a single mode of a quantum electromagnetic
field, to both control and readout the qubit state. At Yale, we
have recently demonstrated (D. Schuster et al.)
that the offresonant
strong coupling between the qubit and the resonator can be used to
perform a quantum nondemolition (QND) dispersive readout
(A. Blais et al.)
of the qubit state. The effective isolation of the
qubit from its environment allowed us to measure one of the
longest coherence times of any charge qubit investigated so far
(D. Schuster et al.).
These properties allow for timeresolved
control and readout of the qubit state, which we have demonstrated
on the single qubit level (A. Wallraff et al.).
In our work at ETH, the coherence of charge
qubits will be investigated using advanced microwave pulse
sequences for performing Ramsey interferometry and spinecho
measurements. Such experiments can be performed efficiently using
the state of the art microwave techniques and large bandwidth data
acquisition systems that we have developed at Yale for the circuit
QED experiments. In the quantum device lab lab we
will identify sources of decoherence with the aim to eliminate
them to a level that error correction becomes feasible. Full
control of the qubit state will be demonstrated. We will realize
coupling of multiple qubits using the resonator as a coupling bus
(A. Blais et al.)
which allows for the implementation of gates similar to the
CiracZoller gates as demonstrated in iontraps. Different
implementations of twoqubit logic and simple gate operations will
be explored. This will allow for the first simple quantum
algorithms to be implemented in a solid state architecture.
The circuit QED qubit readout is predicted to be able to reach
high fidelity and singleshot capability (A. Blais et al.), which
will allow us to investigate correlations in multiqubit systems,
e.g. to determine the fidelity of an entangled state or to
perform a measurement of Bell's inequality. The entanglement of
photons, with qubits, the transfer of entanglement between
different entities, and the use of microwave photons as flying
qubits mediating couplings over large distances, is going to be
studied in my lab. These attractive features make this
architecture a prominent candidate for addressing quantum
computation problems beyond the single qubit level using
techniques that are also applicable to other approaches for solid
state quantum computation.
