Cavity quantum electrodynamics

Short description: Quantum physics of light and matter in a cavity

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Quantum mechanics
iℏ∂∂t|ψ(t)⟩=H^|ψ(t)⟩

Schrödinger equation

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* v
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Cavity Quantum Electrodynamics (cavity QED) is the study of the interaction between light confined in a reflective cavity and atoms or other particles, under conditions where the quantum nature of photons is significant. It could in principle be used to construct a quantum computer.

The case of a single 2-level atom in the cavity is mathematically described by the Jaynes–Cummings model, and undergoes vacuum Rabi oscillations |e⟩|n−1⟩↔|g⟩|n⟩, that is between an excited atom and n−1 photons, and a ground state atom and 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, (α|g⟩+β|e⟩)|0⟩↔|g⟩(α|0⟩+β|1⟩), 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 trapped ion quantum computer and optical quantum communication.

Other interaction durations create entanglement between the atom and cavity field; for example, a quarter-cycle on resonance starting from |e⟩|0⟩ gives the maximally entangled state (a Bell state) (|e⟩|0⟩+|g⟩|1⟩)/2. This can in principle be used as a quantum computer, mathematically equivalent to a trapped ion quantum computer with cavity photons replacing phonons.

## Nobel Prize in Physics

The 2012 Nobel Prize for Physics was awarded to Serge Haroche and David Wineland for their work on controlling quantum systems.[1]

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. doi:10.1088/0034-4885/69/5/R02. Bibcode: 2006RPPh...69.1325W. http://www.iop.org/EJ/abstract/0034-4885/69/5/R02/. 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. doi:10.1088/0953-4075/38/9/007. Bibcode: 2005JPhB...38S.551M. http://www.iop.org/EJ/abstract/0953-4075/38/9/007/. Optical wavelengths, atoms trapped

1. ↑ 1.0 1.1 Johnston, Hamish (9 October 2012). "Quantum-control pioneers bag 2012 Nobel Prize for Physics". Physics World (London). https://physicsworld.com/cws/article/news/2012/oct/09/quantum-control-pioneers-bag-2012-nobel-prize-for-physics.

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Quantum information science

General|

* Quantum computing
* Qubit
* physical vs. logical
* DiVincenzo's criteria
* Quantum information
* Quantum programming
* Quantum processors
* Cloud-based quantum computing
* Timeline of quantum computing

Theorems|

* Bell's theorem
* Gleason's theorem
* Gottesman–Knill theorem
* Holevo's theorem
* Margolus–Levitin theorem
* No-broadcast theorem
* No-cloning theorem
* No-communication theorem
* No-deleting theorem
* No-hiding theorem
* No-teleportation theorem
* PBR theorem
* Quantum threshold theorem

Quantum
communication|

* Quantum capacity
* Classical capacity
* Entanglement-assisted classical capacity
* Quantum channel
* Quantum network
* Quantum cryptography
* Quantum key distribution
* BB84
* SARG04
* Three-stage quantum cryptography protocol
* Quantum teleportation
* Superdense coding
* LOCC
* Entanglement distillation

Quantum algorithms|

* Universal quantum simulator
* Deutsch–Jozsa algorithm
* Grover's algorithm
* Quantum Fourier transform
* Shor's algorithm
* Simon's problem
* Quantum phase estimation algorithm
* Quantum counting algorithm
* Quantum annealing
* Quantum algorithm for linear systems of equations
* Amplitude amplification

Quantum
complexity theory|

* Quantum Turing machine
* EQP
* BQP
* QMA
* PostBQP
* QIP

Quantum
computing models|

* Quantum circuit
* Quantum logic gate
* One-way quantum computer
* cluster state
* Adiabatic quantum computation
* Topological quantum computer

Quantum
error correction|

* Stabilizer codes
* Entanglement-Assisted Quantum Error Correction
* Shor code
* Steane code
* CSS code
* Quantum convolutional codes
* Toric code

Physical
implementations|

| Quantum optics|

* Cavity QED
* Circuit QED
* Linear optical quantum computing
* KLM protocol
* Boson sampling

|

Ultracold atoms|

* Trapped ion quantum computer
* Optical lattice

Spin-based|

* Nuclear magnetic resonance QC
* Kane QC
* Loss–DiVincenzo QC
* Nitrogen-vacancy center

Superconducting
quantum computing|

* Charge qubit
* Flux qubit
* Phase qubit
* Transmon

Software|

* libquantum
* OpenQASM
* Q#
* Qiskit
* IBM Q Experience

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