Exploring quantum supremacy with superconducting circuits.

I will present two projects, based on the use of coupled superconducting resonators, to observe quantum effects:

1. Multiple bosons undergoing coherent evolution in a coupled network of sites constitute a so-called quantum walk system. The simplest example of such a two-particle interference is the celebrated Hong-Ou-Mandel interference. When scaling to larger boson numbers, simulating the exact distribution of bosons has been shown, under reasonable assumptions, to be exponentially hard. We analyze the feasibility and expected performance of a globally connected superconducting resonator based quantum walk system, using the known characteristics of state-of-the-art components. We simulate the sensitivity of such a system to decay processes and to perturbations and compare with coherent input states.

2. Atomic sized two-level systems (TLSs) in dielectrics are known as a major source of loss in superconducting devices, particularly due to frequency noise. However, the induced frequency shifts on the devices, even by far off-resonance TLSs, is often suppressed by symmetry when standard single-tone spectroscopy is used. We introduce a two-tone spectroscopy on the normal modes of a pair of coupled superconducting coplanar waveguide resonators to uncover this effect by asymmetric saturation. Together with an appropriate generalized saturation model this enables us to extract the average single-photon Rabi frequency of dominant TLSs to be Ω₀/2π≈79 kHz. At high photon numbers we observe an enhanced sensitivity to nonlinear kinetic inductance when using the two-tone method and estimate the value of the Kerr coefficient as K/2π≈−1×10⁻⁴Hz/photon. Furthermore, the life-time of each resonance can be controlled (increased) by pumping of the other mode as demonstrated both experimentally and theoretically.