Researchers in many fields of physics have envisaged to couple a
single quantum two-level system coherently to a quantum harmonic
oscillator, see A. Blais et al. and references therein. Until
recently, this feat had only been achieved in the realm of atomic
physics and quantum optics, where a single atom in a ultra high
vacuum is observed to coherently exchange a single photon with a
single mode of a radiation field in atomic cavity quantum
electrodynamics (QED) experiments. Such
experiments have been at the focus of research in atomic physics
and quantum optics in the past decade and have contributed greatly
to our fundamental understanding of the interaction of matter with
quantized electromagnetic fields, of the physics of open quantum
systems and of coherence and decoherence. They are also a major
test ground for developing and demonstrating the general concepts
of quantum information processing.
In a recent experimental breakthrough, covered in the September 9, 2004
issue of Nature (A. Wallraff et al.)
and in the November 2004 issue of Physics Today (M. Wilson),
our group at Yale has demonstrated for the first time that
a solid-state nano-electronic superconducting circuit, acting as
an artificial atom, can be coupled coherently to a single
microwave photon stored in an on-chip cavity.
The success of this approach is based on our ability to design and
fabricate mesoscopic solid-state two-level systems with
controllable properties, such as large effective electric dipole
moments (d ~ 104 e a0), and to develop 1D on-chip cavities
with small mode volumes and very large vacuum electric fields
(E0 ~ 0.1 V/m) leading to large controllable
electric dipole interactions. Key is also the development of
microwave techniques for experiments with mesoscopic devices at
low temperatures. Mastering these techniques, we have realized
this new paradigm of circuit quantum electrodynamics. In
circuit QED coherent quantum optical effects can be observed even
in a solid state environment where coupling to environmental
degrees of freedom leading to decoherence is typically much larger
than in atomic systems.
The circuit QED system developed during my time at
Yale is extremely attractive for fundamental cavity QED
experiments. Its properties can be designed at will in integrated
circuit fabrication and tuned in situ in experiment while allowing
for extremely large coupling strengths. At the same time our
artificial atom is deterministically at a fixed position within
the cavity, avoiding fluctuations in the coupling strength. These
are major advantages in comparison to atomic cavity QED. Thus this
circuit QED system has great prospects to enable experiments that
complement existing work and go beyond the current state of the
art of atomic cavity QED. We plan to address fundamental quantum
optics questions, applications in quantum
computation and the use of this architecture
as a sensitive measurement device or detector in our work.