Resolving photon number states in a superconducting circuit

By David I. Schuster, Andrew A. Houck, J. Schreier, Andreas Wallraff, Jay M. Gambetta, Alexandre Blais, Luigi Frunzio, J. Majer, Blake R. Johnson, Michel H. Devoret and 2 more. Nature, 2006

769 citations recorded by the source corpus.

Electromagnetic signals are always composed of photons, although in the circuit domain those signals are carried as voltages and currents on wires, and the discreteness of the photon's energy is usually not evident. However, by coupling a superconducting quantum bit (qubit) to signals on a microwave transmission line, it is possible to construct an integrated circuit in which the presence or absence of even a single photon can have a dramatic effect. Such a system can be described by circuit quantum electrodynamics (QED)—the circuit equivalent of cavity QED, where photons interact with atoms or quantum dots. Previously, circuit QED devices were shown to reach the resonant strong coupling regime, where a single qubit could absorb and re-emit a single photon many times. Here we report a circuit QED experiment in the strong dispersive limit, a new regime where a single photon has a large effect on the qubit without ever being absorbed. The hallmark of this strong dispersive regime is that the qubit transition energy can be resolved into a separate spectral line for each photon number state of the microwave field. The strength of each line is a measure of the probability of finding the corresponding photon number in the cavity. This effect is used to distinguish between coherent and thermal fields, and could be used to create a photon statistics analyser. As no photons are absorbed by this process, it should be possible to generate non-classical states of light by measurement and perform qubit–photon conditional logic, the basis of a logic bus for a quantum computer.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/45ea4adbb1b8feb9b46139682738c36f5cd39e7a

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Citations in the corpus

The quantum-optical Josephson interferometer (2008, result): “2 2C4 2( J)U 2 ( 4 ) where D C 2 and ( J)D(4 J2C )=(4 J2C 2). These results are consistent with the expectation that strong photon nonlinearity can lead to photon blockade1 in the central cavity, giving rise to antibunching.”
Microwave photonics with superconducting quantum circuits (2017, background): “This regime is known as the number-splitting regime, since the qubit spectrum resolves individual photon-number states [365, 374].”
Colloquium: Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits (2011, background): “The build-up of photons in a cavity with sinusoidally modulated length was studied in e.g. (Dodonov and Klimov, 1996; Dodonov et al., 1990, 1993; Ji et al., 1997; Schützhold et al., 1998).”
Demonstration of two-qubit algorithms with a superconducting quantum processor (2009, background): “Operation in the strong-dispersive regime 27 of cQED allows joint readout 28 that can eﬃ-ciently detect two-qubit correlations.”
New class of quantum error-correcting codes for a bosonic mode (2016, background): “In the strong-dispersive limit, where the strength of the dispersive coupling χ is greater than the decay rates of the qubit and the cavity, one can drive the qubit conditioned on given photon number states of the cavity [116,117].”
Quantum information processing and quantum optics with circuit quantum electrodynamics (2020, background): “As alluded to in the previous section, this very large light shift enables sophisticated quantum control capabilities, something which we come back to below.”