Chiral quantum optics with giant atoms

Abstract

In quantum optics, it is common to assume that atoms are point-like objects compared to the wavelength of the electromagnetic field they interact with. However, this dipole approximation is not always valid, e.g., if atoms couple to the field at multiple discrete points. Previous work has shown that superconducting qubits coupled to a one-dimensional waveguide can behave as such "giant atoms" and then can interact through the waveguide without decohering, a phenomenon that is not possible with small atoms. Here, we show that this decoherence-free interaction is also possible when the coupling to the waveguide is chiral, i.e., when the coupling depends on the propagation direction of the light. Furthermore, we derive conditions under which the giant atoms in such chiral architectures exhibit dark states. In particular, we show that unlike small atoms, giant atoms in a chiral waveguide can reach a dark state even without being excited by a coherent drive. We also show that in the driven-dissipative regime, dark states can be populated faster in giant atoms. The results presented here lay a foundation for applications based on giant atoms in quantum simulations and quantum networks with chiral settings.

Non-perturbative treatment of giant atoms using chain transformations

“…In particular giant atoms challenge standard approximations and can only be accurately described when taking the finite spatial extent of the artificial atom into account, plus a finite propagation speed if coupled to sound waves [3,4] and counter-rotating terms beyond the rotating-wave approximation (RWA) at strong couplings. Recent work has already capitalized on this and demonstrated several intruiging effects that occur in giant atomic setups, including decoherence-free interactions [5], non-exponential atomic decay [6], oscillating bound states [7] and chiral atom-waveguide couplings [8]. Still theoretical treatment has so far been restricted to couplings in the realm of the RWA.…”

Giant atoms with time-dependent couplings

“…While the interaction at each atom-field coupling point can still be well described by the dipole approximation, the atoms in these systems can no longer be viewed as points and the phase accumulations of photons between different coupling points should be taken into account. To date, there have been a variety of intriguing phenomena witnessed in giant-atom structures, such as frequency-dependent Lamb shifts and relaxation rates [8], decoherence-free interatomic interactions [9,[11][12][13][14], unconventional bound states [15][16][17][18][19][20][21], and phase-controlled frequency conversions [22,23]. Most recently, giant atoms have also been extended to the nonperturbative regime [24], to chiral quantum optics [12-15, 25, 26], and to synthetic dimensions [27].…”

Chiral Quantum Network with Giant Atoms

“…In SQC platform, the giant atoms, which size are comparable to the wavelength of the coupled photonic mode [43][44][45][46][47][48][49][50][51], can be realized by considering multiple coupling points with a photonic (or phononic) waveguide [52].…”

“…The interference effects between different points will lead to exotic quantum phenomena such as frequency-dependent emission, and dipole-dipole interactions free of decoherence [43,45,51]. Moreover, the fast dark state preparation is also discussed in a chiral quantum system with giant atoms [51]. However, how to realize such chiral quantum networks is rarely discussed currently.…”