Special CPM Seminar

Exploring the Quantum Properties of Propagating Microwave Fields

Andreas Wallraff

ETH Zurich

Using modern micro and nano-fabrication techniques combined with superconducting materials we realize quantum electronic circuits in which we create, store, and manipulate individual microwave photons. Making use of the strong interaction engineered between photons and superconducting quantum two-level systems we probe fundamental quantum effects of microwave radiation and develop components for applications in quantum technology. We routinely realize both pulsed [1] and continuously pumped [2] microwave frequency single photon sources which we characterize using correlation function measurements [3] and full quantum state tomography [4]. For this purpose we develop efficient methods to separate the quantum signals of interest from the noise added by the linear amplifiers used for quadrature amplitude detection [5]. We employ superconducting parametric amplifiers [6,7] to perform nearly quantum limited detection of propagating microwave fields. Using such amplifiers we probe the entanglement which we generate on demand between stationary qubits and microwave photons freely propagating down a transmission line [8]. Using two independent microwave single photon sources we perform Hong-Ou-Mandel experiments at microwave frequencies [9] and probe the coherence of two-mode multi-photon states at the out-put of a beam-splitter. The non-local nature of such states may prove to be useful for distributing entanglement in future small-scale quantum networks.

[1] D. Bozyigit et al., Nat. Phys. 7, 154 (2011)
[2] C. Lang et al., Phys. Rev. Lett. 106, 243601 (2011)
[3] M. P. da Silva, Phys. Rev. A 82, 043804 (2010)
[4] C. Eichler et al., Phys. Rev. Lett. 106, 220503 (2011)
[5] C. Eichler et al., Phys. Rev. A 86, 032106 (2012)
[6] C. Eichler et al., Phys. Rev. Lett. 107, 113601 (2011)
[7] C. Eichler et al., arXiv:1404.4643 (2014)
[8] C. Eichler et al., Phys. Rev. Lett. 109, 240501 (2012)
[9] C. Lang et al., Nat. Phys. 9, 345-348 (2013)