Per Delsing

Observation of the dynamical Casimir effect in a superconducting circuit

One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. Although initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences—for instance, producing the Lamb shift of atomic spectra and modifying the magnetic moment of the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed whether it might be possible to more directly observe the virtual particles that compose the quantum vacuum. Forty years ago, it was suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. The phenomenon, later termed the dynamical Casimir effect, has not been demonstrated previously. Here we observe the dynamical Casimir effect in a superconducting circuit consisting of a coplanar transmission line with a tunable electrical length. The rate of change of the electrical length can be made very fast (a substantial fraction of the speed of light) by modulating the inductance of a superconducting quantum interference device at high frequencies (>10 gigahertz). In addition to observing the creation of real photons, we detect two-mode squeezing in the emitted radiation, which is a signature of the quantum character of the generation process.

Evidence for coexistence of the superconducting gap and the pseudogap in Bi-2212 from intrinsic tunneling spectroscopy.

We present intrinsic tunneling spectroscopy measurements on small Bi

Demonstration of a Single-Photon Router in the Microwave Regime

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Current measurement by real-time counting of single electrons

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Tuning the field in a microwave resonator faster than the photon lifetime

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Coherent dynamics of a Josephson charge qubit

CaCu

Propagating phonons coupled to an artificial atom

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A concept for a submillimeter-wave single-photon counter

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Giant cross-Kerr effect for propagating microwaves induced by an artificial atom

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Radio-frequency single-electron transistor: Toward the shot-noise limit

mesas. The tunnel conductance curves show both sharp peaks at the superconducting gap voltage and broad humps representing the