Controllable Switching between Superradiant and Subradiant States in a 10-qubit Superconducting Circuit

Abstract

Superradiance and subradiance concerning enhanced and inhibited collective radiation of an ensemble of atoms have been a central topic in quantum optics. However, precise generation and control of these states remain challenging. Here we deterministically generate up to 10-qubit superradiant and 8-qubit subradiant states, each containing a single excitation, in a superconducting quantum circuit with multiple qubits interconnected by a cavity resonator. The √ N -scaling enhancement of the coupling strength between the superradiant states and the cavity is validated. By applying appropriate phase gate on each qubit, we are able to switch the single collective excitation between superradiant and subradiant states. While the subradiant states containing a single excitation are forbidden from emitting photons, we demonstrate that they can still absorb photons from the resonator. However, for even number of qubits, a singlet state with half of the qubits being excited can neither emit nor absorb photons, which is verified with 4 qubits. This study is a step forward in coherent control of collective radiation and has promising applications in quantum information processing.

Photon-Mediated Localization in Two-Level Qubit Arrays

“…The "cross shape" means that the motion is highly constrained for the first excitation and free to propagate in space for the second excitation, or vice versa. We demonstrate that such cross-shaped states arise naturally for subwavelength arrays in a broad range of parameters which should be experimentally observable in systems where the qubits are probed individually [3].…”

“…Introduction. Many-body quantum optical systems have received intense interest in the recent years due to ground-breaking experiments with superconducting qubits [1][2][3] and cold atoms coupled to waveguides [4]. A paradigmatic system in quantum optics is an array of atoms coupled to freely propagating photons [5][6][7].…”

Quasiflat band enabling subradiant two-photon bound states

“…The array of atoms coupled to freely propagating photons is a paradigmatic system for quantum optics, well known at least since the work of Dicke in 1954 [2][3][4][5]. However, recent technological advances with the cold atom [6] and superconducting qubit [7][8][9] systems have revived and boosted interest to this problem underlining its importance for future quantum technologies [10][11][12][13]. Specifically, it has been understood that the new collective many-body effects emerge when the distance between the atoms is varied.…”

Radiative topological biphoton states in modulated qubit arrays

“…Strong photon-photon interactions [12,13] are known to appear in photonic waveguides coupled to atoms [23] or arrays of superconducting qubits [24][25][26]. These quantum waveguides support various exotic correlated states, such as photon bound states [27], novel twilight states [28], and selfinduced localized states [29], which look very promising for storage and processing of quantum information.…”