Cavity quantum electrodynamics

Cavity quantum electrodynamics (cavity QED) is the study of the interaction between light confined in a reflective

The case of a single 2-level atom in the cavity is mathematically described by the Jaynes–Cummings model, and undergoes vacuum Rabi oscillations ${\displaystyle |e\rangle |n-1\rangle \leftrightarrow |g\rangle |n\rangle }$, that is between an excited atom and ${\displaystyle n-1}$ photons, and a ground state atom and ${\displaystyle n}$ photons.

If the cavity is in resonance with the atomic transition, a half-cycle of oscillation starting with no photons coherently swaps the atom qubit's state onto the cavity field's, ${\displaystyle (\alpha |g\rangle +\beta |e\rangle )|0\rangle \leftrightarrow |g\rangle (\alpha |0\rangle +\beta |1\rangle )}$, and can be repeated to swap it back again; this could be used as a single photon source (starting with an excited atom), or as an interface between an atom or

Other interaction durations create entanglement between the atom and cavity field; for example, a quarter-cycle on resonance starting from ${\displaystyle |e\rangle |0\rangle }$ gives the

) ${\displaystyle (|e\rangle |0\rangle +|g\rangle |1\rangle )/{\sqrt {2}}}$. This can in principle be used as a

trapped ion quantum computer

with cavity photons replacing phonons.

Nobel Prize in Physics

The

Haroche shares half of the prize for developing a new field called cavity quantum electrodynamics (CQED) – whereby the properties of an atom are controlled by placing it in an optical or microwave cavity. Haroche focused on microwave experiments and turned the technique on its head – using CQED to control the properties of individual photons.[1]

In a series of ground-breaking experiments, Haroche used CQED to realize Schrödinger's famous cat experiment in which a system is in a superposition of two very different quantum states until a measurement is made on the system. Such states are extremely fragile, and the techniques developed to create and measure CQED states are now being applied to the development of quantum computers.

See also

• Circuit quantum electrodynamics
• Superconducting radio frequency
• Dicke model

References

• Herbert Walther; Benjamin T H Varcoe; Berthold-Georg Englert; Thomas Becker (2006). "Cavity quantum electrodynamics". Rep. Prog. Phys. 69 (5): 1325–1382.
  S2CID 122420445
  . Microwave wavelengths, atoms passing through cavity
• R Miller; T E Northup; K M Birnbaum; A Boca; A D Boozer; H J Kimble (2005). "Trapped atoms in cavity QED: coupling quantized light and matter". J. Phys. B: At. Mol. Opt. Phys. 38 (9): S551–S565.
  S2CID 1114899
  . Optical wavelengths, atoms trapped