Strong Coupling Cavity QED with Gate-Defined Double Quantum Dots Enabled by a High Impedance Resonator

Abstract

The strong coupling limit of cavity quantum electrodynamics (QED) implies the capability of a matter-like quantum system to coherently transform an individual excitation into a single photon within a resonant structure. This not only enables essential processes required for quantum information processing but also allows for fundamental studies of matter-light interaction. In this work we demonstrate strong coupling between the charge degree of freedom in a gate-defined GaAs double quantum dot (DQD) and a frequency-tunable high impedance resonator realized using an array of superconducting quantum interference devices (SQUIDs). In the resonant regime, we resolve the vacuum Rabi mode splitting of size 2g/2π = 238 MHz at a resonator linewidth κ/2π = 12 MHz and a DQD charge qubit dephasing rate of γ2/2π = 80 MHz extracted independently from microwave spectroscopy in the dispersive regime. Our measurements indicate a viable path towards using circuit based cavity QED for quantum information processing in semiconductor nano-structures.In the strong coupling limit, cavity QED realizes the coherent exchange of a single quantum of energy between a nonlinear quantum system with two or more energy levels, e.g. a qubit, and a single mode of a high quality cavity capable of storing individual photons [1]. The distinguishing feature of strong coupling is a coherent coupling rate g, determined by the product of the dipole moment of the multi-level system and the vacuum field of the cavity, which exceeds both the cavity mode linewidth κ, determining the photon life time, and the qubit linewidth γ 2 = γ 1 /2 + γ ϕ , set by its energy relaxation and pure dephasing rates, γ 1 and γ ϕ , respectively.The strong coupling limit of Cavity QED has been reached with a multitude of physical systems including alkali atoms [2], Rydberg atoms [3], superconducting circuits [4,5] and optical transitions in semiconductor quantum dots [6,7]. Of particular interest is the use of this concept in quantum information processing with supercondcuting circuits where it is known as circuit QED [4,8,9].Motivated by the ability to suppress the spontaneous emission of qubits beyond the free space limit [10], to perform quantum non-demolition (QND) qubit read-out [11,12], to couple distant qubits through microwave photons coherently [13,14] and to convert quantum information stored in stationary qubits to photons [15,16], research towards reaching the strong coupling limit of cavity QED is pursued for the charge and spin degrees of freedom in semiconductor nano-structures [17][18][19][20][21][22]. Recently, in parallel with the work discussed here, independent efforts to reach this goal have come to fruition with gate defined DQDs in silicon [23] and carbon nanotubes [24].The essence of our approach to reach the strong coupling limit with individual electronic charges in GaAs DQDs is rooted in the enhancement of the electric component of the vacuum fluctuations ∝ √ Z r [25] by increas-ing the resonator impedance Z r beyond the typical 50 Ω of a standard copl...

Cavity QED with hybrid nanocircuits: from atomic-like physics to condensed matter phenomena

“…b. Strong coupling limit Very recently, the strong coupling regime was reached simultaneously in three experiments based on different types of charge double quantum dots [30][31][32] . In this regime, for a low number of photons ñ → 0, the cavity transmission (or reflection) amplitude versus the frequency excitation ω RF shows a double peak, due to the strong hybridization between the cavity and the L/R charge degree of freedom of the double dot (see Fig.9d).…”

Noise switching at a dynamical critical point in a cavity-conductor hybrid

“…Recent experiments on such systems, using conductors such as Josephson junction (JJ) devices [1][2][3], or quantum dots [4,5], have demonstrated that coherent interactions between a conductor and a cavity can generate large non-equilibrium photon populations. Parallels can be drawn between cavity-conductor hybrids and quantum optical devices such as the micromaser in which a stream of excited atoms flows through an optical cavity [6,7]; in both cases the photons in the cavity act back on the photon generation process leading to strongly nonlinear dynamics and dissipative phase transitions.…”

Approaching ultrastrong coupling in transmon circuit QED using a high-impedance resonator

“…Using a high-impedance Z 0 considerably increases coupling rates compared to typical 50 implementations by increasing the voltage zero-point fluctuations of the cavity V zpf ∝ √ Z 0 as exploited in cavity QED with quantum dots [19]. When the transmon and fundamental mode of the cavity are resonant, we spectroscopically measure a coupling g/2π = 455 MHz, corresponding toḡ = 0.071.…”