Abstract The hybrid circuit quantum electrodynamics architecture integrated quantum dots with a microwave resonator results in the creation of a controllable artificial system and enriches its physics through electron–photon interaction. In this study, a hybrid device is investigated, wherein a triple quantum dot (TQD) is dipole coupled with electric field of a superconducting quantum interference device array resonator. The quantum cellular automata (QCA) process of TQD, related to charge reconfiguration as a result of Coulomb interaction between each dot, is observed by probing reflectance of the resonator. The suppressed cavity reflectance signal of the QCA process may experimentally provide the evidence for the different measurement mechanism of the cavity from external electrometers like quantum point contact. Furthermore, on careful tuning of multiple energy level differences of the TQD to match the cavity photon frequency, four tunneling processes assisted by the absorption of the cavity photons occur simultaneously, contributing to “photon‐assisted” quadruple point. Consequently, these two specific phenomena are found to be closely dependent on the relationship between the various Coulomb energy in TQD and the cavity photon energy. The results are consistent with the theoretical model presented and imply that this hybrid system has the potential for investigating exotic many‐body effects and matter–light interaction.
Abstract The hybrid circuit quantum electrodynamics architecture integrated quantum dots with a microwave resonator results in the creation of a controllable artificial system and enriches its physics through electron–photon interaction. In this study, a hybrid device is investigated, wherein a triple quantum dot (TQD) is dipole coupled with electric field of a superconducting quantum interference device array resonator. The quantum cellular automata (QCA) process of TQD, related to charge reconfiguration as a result of Coulomb interaction between each dot, is observed by probing reflectance of the resonator. The suppressed cavity reflectance signal of the QCA process may experimentally provide the evidence for the different measurement mechanism of the cavity from external electrometers like quantum point contact. Furthermore, on careful tuning of multiple energy level differences of the TQD to match the cavity photon frequency, four tunneling processes assisted by the absorption of the cavity photons occur simultaneously, contributing to “photon‐assisted” quadruple point. Consequently, these two specific phenomena are found to be closely dependent on the relationship between the various Coulomb energy in TQD and the cavity photon energy. The results are consistent with the theoretical model presented and imply that this hybrid system has the potential for investigating exotic many‐body effects and matter–light interaction.
Abstract Scaling up spin qubits in silicon-based quantum dots is one of the pivotal challenges in achieving large-scale semiconductor quantum computation. To satisfy the connectivity requirements and reduce the lithographic complexity, utilizing the qubit array structure and the circuit quantum electrodynamics (cQED) architecture together is expected to be a feasible scaling scheme. A triple-quantum dot (TQD) coupled with a superconducting resonator is regarded as a basic cell to demonstrate this extension scheme. In this article, we investigate a system consisting of a silicon TQD and a high-impedance TiN coplanar waveguide (CPW) resonator. The TQD can couple to the resonator via the right double-quantum dot (RDQD), which reaches the strong coupling regime with a charge–photon coupling strength of g 0/(2π) = 175 MHz. Moreover, we illustrate the high tunability of the TQD through the characterization of stability diagrams, quadruple points (QPs), and the quantum cellular automata (QCA) process. Our results contribute to fostering the exploration of silicon-based qubit integration.
A double quantum dot defines a qubit by a two-level system. The coupling between two qubits induces a double two-level system into a four-level system. We study experimentally the coupling between two capacitive coupled GaAs/AlGaAs double quantum dots while tuning the energy detuning of each double quantum dot simultaneously. Applying microwave photons (at a frequency of 20 GHz) on this system and observing the resonance tunneling with a quantum point contact detector, we obtain an excitation spectrum which is consistent with the numerical simulation result of a coupled two-qubit Hamiltonian. This study demonstrates that a double quantum dot can be exploited as an extraordinary platform for controlled quantum gates.
We have realized a hybrid solid-state quantum device in which a single-electron semiconductor double quantum dot is dipole coupled to a superconducting microwave frequency transmission line resonator. The dipolar interaction between the two entities manifests itself via dispersive and dissipative effects observed as frequency shifts and linewidth broadenings of the photonic mode respectively. A Jaynes-Cummings Hamiltonian master equation calculation is used to model the combined system response and allows for determining both the coherence properties of the double quantum dot and its interdot tunnel coupling with high accuracy. The value and uncertainty of the tunnel coupling extracted from the microwave read-out technique are compared to a standard quantum point contact charge detection analysis. The two techniques are found to be consistent with a superior precision for the microwave experiment when tunneling rates approach the resonator eigenfrequency. Decoherence properties of the double dot are further investigated as a function of the number of electrons inside the dots. They are found to be similar in the single-electron and many-electron regimes suggesting that the density of the confinement energy spectrum plays a minor role in the decoherence rate of the system under investigation.
We fabricate and characterize a hybrid quantum device that consists of five gate-defined double quantum dots (DQDs) and a high-impedance NbTiN transmission resonator. The controllable interactions between DQDs and the resonator are spectroscopically explored by measuring the microwave transmission through the resonator in the detuning parameter space. Utilizing the high tunability of the system parameters and the high cooperativity ( C total > 17.6) interaction between the qubit ensemble and the resonator, we tune the charge-photon coupling and observe the collective microwave response changing from linear to nonlinear. Our results present the maximum number of DQDs coupled to a resonator and manifest a potential platform for scaling up qubits and studying collective quantum effects in semiconductor–superconductor hybrid cavity quantum electrodynamics systems.
We theoretically study a silicon triple quantum dot (TQD) system coupled to a superconducting microwave resonator. The response signal of an injected probe signal can be used to extract information about the level structure by measuring the transmission and phase shift of the output field. This information can further be used to gain knowledge about the valley splittings and valley phases in the individual dots. Since relevant valley states are typically split by several [Formula: see text], a finite temperature or an applied external bias voltage is required to populate energetically excited states. The theoretical methods in this paper include a capacitor model to fit experimental charging energies, an extended Hubbard model to describe the tunneling dynamics, a rate equation model to find the occupation probabilities, and an input-output model to determine the response signal of the resonator.
Coupling on-chip microwave cavities to superconducting microcircuits has provided a new platform to study the light/matter interaction at the most elementary level [1]. Coupling such cavities to more complex quantum circuits, like quantum dot circuits, is of high interest since it would allow the use of different degrees of freedom, like for instance the electronic spin, in a cavity quantum electrodynamics context. In this talk, I will present various theoretical proposals which would exploit this possibility. First, I will present a scheme allowing a strong coupling between cavity photons and a single spin trapped in a double quantum dot with ferromagnetic contacts [2]. Such a scheme would enable a scalable spin quantum bit architecture. Second, I will discuss theoretically the coupling of a double-quantum dot based Cooper pair splitter to a cavity [3]. Such a scheme can be used to test the entanglement of split Cooper pairs, due to a subradiance property of the Cooper pairs singlet state. Third, I will present recent experiments on carbon nanotube based quantum dots coupled to microwave cavities. In particular, I will discuss the observation of a charge coupling between two distant quantum dots mediated by cavity photons. [1] A. Wallraff, D. I. Schuster, A. Blais, L. Frunzio, R.- S. Huang, J. Majer, S. Kumar, S.M. Girvin, and R. J. Schoelkopf, Nature (London) 431, 162 (2004). [2] A. Cottet and T. Kontos, Phys. Rev. Lett. 105, 160502 (2010) [3] A. Cottet, T. Kontos, and A. Levy Yeyati, Phys. Rev. Lett. 108, 166803 (2012). [5] M.R. Delbecq, V. Schmitt, F.D. Parmentier, N. Roch, J.J. Viennot, G. Fève, B. Huard, C. Mora, A. Cottet, and T. Kontos, Phys. Rev. Lett. 107,256804 (2011) [6] M.R. Delbecq et al., unpublished