Control of Collective Dark States in Waveguide QED

Julian Daser,

Teresa Hönigl-Decrinis, Gerhard Kirchmair



Institute for Experimental Physics, University of Innsbruck, 6020 Innsbruck, Austria

&

Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, 6020 Innsbruck, Austria



julian.daser@uibk.ac.at,

Propagating microwave photons in waveguides couple well to superconducting qubits and mediate long-range interactions between distant qubits causing the emergence of collective states due to interference effects [1]. Of particular interest are dark or subradiant states, which are protected from decoherence as they decouple from the waveguide environment and thus exhibit long lifetimes. This makes them promising candidates for photon storage, excitation transfer and photon-photon gates [2].

However, the protection from decoherence comes with a caveat that the control of such states is challenging. Only recently, a collective dark state formed by two transmon pairs, each pair also exhibiting a local dark state, was probed experimentally by exciting selectively through individual drive ports in a rectangular waveguide [3].

To extend the system to larger arrays of transmon qubits [2,4], we are working on a planar implementation. The goal is to have 8 Transmon qubits, coupled to a coplanar waveguide. The qubits will be spaced out by a distance that corresponds to half of the emission wavelength. In such a system it will be possible to create subradiant states with up to four excitations [2].

References

[1] Sheremet, A. S., et al. Rev. Mod. Phys. 95, 015002 (2023)

[2] Holzinger, R., et al., Phys. Rev. Let. 129, 253601 (2022)

[3] Zanner, M., et al., Nature Physics 18, 538-543 (2022)

[4] Orell, T., et al. Phys. Rev. A 105.6, 063701 (2022)