Towards high-cooperativity strong coupling of a quantum dot in a tunable microcavity

Abstract

We investigate the strong coupling regime of a self-assembled quantum dot in a tunable microcavity with dark-field laser spectroscopy. The high quality of the spectra allows the lineshapes to be analyzed revealing subtle quantum interferences. Agreement with a model calculation is achieved only by including exciton dephasing which reduces the cooperativity from a bare value of 9.0 to the time-averaged value 5.5. In the pursuit of high cooperativity, besides a high-Q and low modevolume cavity, we demonstrate that equal efforts need to be taken towards lifetime-limited emitter linewidths.Cavity quantum electrodynamics (QED) involves an exchange of energy quanta between a single emitter and a cavity photon. The coupling ratehg = µ 12 E vac , depending on the emitter's dipole moment µ 12 and the vacuum electric field at the location of the emitter E vac , sets the relevant timescale of the coupled dynamics. If g is considerably smaller than the emitter relaxation rate γ or the cavity photon decay rate κ, on resonance the cavity mode acts as an additional decay channel to the emitter giving rise to an enhanced spontaneous emission rate (the Purcell effect of the weak coupling regime). If g is much larger than the energy loss rates, a coherent exchange of energy quanta takes place giving rise to new eigenstates, "polaritons", split in energy by 2hg (the strong coupling regime). The efficacy of the coherent coupling is commonly denoted by the cooperativity parameter C = 2g 2 /(κγ), the figure of merit for this work. The coherent exchange was first realized with single Cs atoms in a high finesse cavity [1].The strong coupling regime is a potentially powerful tool in quantum information processing [2], notably in quantum networks [3], since it enables for instance atomatom entanglement [4] or the distribution of quantum states [5]. Furthermore, strong coupling enables a nonlinear photon-photon interaction and hence the observation of photon blockade [6,7], a prerequisite for the creation of a single photon transistor [8,9].It is clearly desirable to implement cavity-QED in the solid-state as the solid-state host acts as a natural trap for the emitter. Furthermore, on-chip integration of multiple elements is feasible. As emitter, self-assembled quantum dots have desirable properties: high oscillator strength, narrow linewidths and weak phonon coupling [10]. As host, a semiconductor such as GaAs is very versatile: heterostructures can be realized; there is a wide array of post-growth processing techniques. Photoluminescence experiments on single InGaAs SAQD coupled to a photonic crystal cavity or a micropillar cavity revealed an anticrossing, the signature of the strong coupling regime [11][12][13]. For micropillars, recent experiments exhibit cooperativity values of around C 3 [14]. For photonic crystal cavities, a much higher C is achieved [15] but C is skewed by the fact that g γ yet g > ∼ κ.The photon decay rate κ at the emitter wavelength is relatively high in both geometries, limiting the cooperativity. In addition, ...

Fabrication of mirror templates in silica with micron-sized radii of curvature

“…6 Already, significant emitter-cavity cooperativity has been achieved with scaled down dimensions. 7 For these tunable plano-concave microcavities, the route to high coupling rates lies within the strong confinement of the resonant mode which is achieved by reducing the curved mirror's radius of curvature (R).…”

Ultrawide electrical tuning of light matter interaction in a high electron mobility transistor structure

“…Interestingly, in our experiment the bare cavity resonance is present in the range of voltages where the coupling regime lies and beyond. The presence of the uncoupled resonator signal at the anticrossing point has been reported before in atom-cavity system48 and its solid-state analogues such as quantum dot-cavity systems649. While in the atom-cavity system this is a result of the fluctuation in the number of atoms in the cavity, in case of dot-cavity systems it is due to the fluctuation of the emitter energy over time.…”

“…While in the atom-cavity system this is a result of the fluctuation in the number of atoms in the cavity, in case of dot-cavity systems it is due to the fluctuation of the emitter energy over time. Following a similar chain of arguments, our system is a solid-state analogue where the quantum well replaces the quantum dot and the metamaterials replace the photonic crystal6 or Fabry Pérot cavity49. The fluctuation in the emitter energy results from the fluctuation of the gate voltage since the frequency of the intersubband transitions depends very sensitively on the applied gate voltage and hence on the carriers.…”

Superconducting resonator and Rydberg atom hybrid system in the strong coupling regime

“…3(a), the energy spacing of one-photon anticrossing happening between | ↓, N +1 and | ↑, N at E s = E (c) s ≡ 543.3 V/cm (the superscript c denotes the atom-resonator coupling) approximates √ N + 1g, where g 2| ↓, 1|V o / | ↑, 0 | is the single photon-atom interaction strength. For our physical specification, g approximates 2π × 0.90 GHz, larger than any coupling strengths achieved in recently experimentally demonstrated atom-cavity and SC qubitresonator systems [32][33][34][35][36][37][38][39][40][41][42][43] and almost equal to that of the atom-waveguide system [44,45]. Similar to the nonlinearity introduced by integrating JJs into the LC circuit, the strong atom-resonator coupling disturbs the harmonic potential of LC resonator and makes | ↓, N +1 and | ↑, N well separated from others around E (c) s , resulting in the SC dressed-state qubits [14].…”