Subradiant states of quantum bits coupled to a one-dimensional waveguide

Abstract

The properties of coupled emitters can differ dramatically from those of their individual constituents. Canonical examples include sub-and super-radiance, wherein the decay rate of a collective excitation is reduced or enhanced due to correlated interactions with the environment. Here, we systematically study the properties of collective excitations for regularly spaced arrays of quantum emitters coupled to a one-dimensional waveguide. We find that, for low excitation numbers, the modal properties are well-characterized by spin waves with a definite wavevector. Moreover, the decay rate of the most subradiant modes obeys a universal scaling with a cubic suppression in the number of emitters. Multiexcitation subradiant eigenstates can be built from fermionic combinations of single excitation eigenstates; such 'fermionization' results in multiple excitations that spatially repel one another. We put forward a method to efficiently create and measure such subradiant states, which can be realized with superconducting qubits. These measurement protocols probe both real-space correlations (using on-site dispersive readout) and temporal correlations in the emitted field (using photon correlation techniques).

Subradiance-protected excitation transport

“…An alternative approach that allows subradiant states to emerge for large ratios a/λ is changing the radiation field's boundary conditions by placing, e.g. a surface or a waveguide [33,[55][56][57][58][59][60][61][62] near the atoms, which in turn modifies the exchange interaction and dissipation. Another experimental challenge is the preparation of the subradiant wave packets.…”

Quasiclassical modeling of cavity quantum electrodynamics

“…In confined geometries such as nanoscale cavities, the quantum nature of photons can strongly modify the properties of atoms and molecules, including the control of spontaneous emission rates [1][2][3][4], frequency splitting of the absorption spectrum due to strong light-matter coupling [5,6], and changes in chemical reaction landscapes by forming hybrid light-matter states (molecular polaritons) [7][8][9][10][11][12]. In the field of cavity quantum electrodynamics (cQED), theorists traditionally describe these phenomena by adapting simplified quantum models, such as the Jaynes-Cummings (JC) model [13] [i.e., a two-level system (TLS) coupled to a single cavity photon mode], the Tavis-Cummings (TC) model [14,15] (i.e., N TLSs coupled to a single photon mode), or the Weisskopf-Wigner model [16] (i.e., a TLS coupled to M photon modes within the context of a single excitation manifold).…”

Quasiflat band enabling subradiant two-photon bound states

“…Specifically, it has been understood that the new collective many-body effects emerge when the distance between the atoms is varied. The physics of single-excited states is relatively straightforward: in the subwavelength case there exist multiple strongly subradiant modes with the radiative lifetime scaling as N 3 /d 2 with the number of atoms N and the spacing d [14]. However, the two-particle subradiant excitations appear to be significantly more complex due to the photon blockade that forbids double excitation of a single atom.…”