Hybrid quantum systems

Light-matter interactions at the single particle level have generally been explored in the context of atomic, molecular, and optical physics. Recent advances motivated by quantum information science have made it possible to explore coherent interactions between photons trapped in superconducting cavities and superconducting qubits. Spins in semiconductors can have exceptionally long spin coherence times and can be isolated in silicon, the workhorse material of the semiconductor microelectronic industry.

Recently, the regime of strong coupling of cavity quantum electrodynamics (QED) between an electron spin qubit and a superconducting microwave resonator has been achieved, opening many new possibilities and raising a number of scientific questions [1]. The role of the quantum two-level system can be played by a single electron spin in a double quantum dot under the influence of an inhomogeneous magnetic field in the “flopping mode” [2], as experimentally demonstrated in [3,4] (see Figure below). Alternatively, a resonant-exchange (RX) spin qubit may replace the spin ½ of a single spin as the qubit, offering full electric control [5,6].

Figure Vacuum Rabi splitting originating from the strong coupling of the spin of an electron in a double quantum dot embedded into the superconducting resonator, as detected in cavity transmission. (a) Cavity transmission A calculated with input-output theory [1,2]. The detuning Δ0 of the probe field from the cavity resonance determines the transmission far off-resonance with the spin qubit. The magnetic field Bz tunes the Zeeman splitting of the spin into resonance with the cavity. (b) Measured cavity transmission [3].

[1] G. Burkard, M. J. Gullans, X. Mi, and J. R. Petta, Nature Rev. Phys. 2, 129 (2020).
[2] M. Benito, X. Mi, J. M. Taylor, J. R. Petta, and G. Burkard, Phys. Rev. B 96, 235434 (2017)
[3] X. Mi, M. Benito, S. Putz, D. M. Zajac, J. M. Taylor, G. Burkard, and J. R. Petta, Nature 555, 599 (2018)
[4] N. Samkharadze, G. Zheng, N. Kalhor, D. Brousse, A. Sammak, U. C. Mendes, A. Blais, G. Scappucci, and L. M. K. Vandersypen, Science 359, 1123 (2018)
[5] A. J. Landig, J. V. Koski, P. Scarlino, U. C. Mendes, A. Blais, C. Reichl, W. Wegscheider, A. Wallraff, K. Ensslin, and T. Ihn, Nature 560, 179 (2018)
[6] M. Russ and G. Burkard, Phys. Rev. B 91, 235411 (2015); Phys. Rev. B 92, 205412 (2015)