We propose theoretically a scheme for implementing a spin quantum bit in a quantum dot circuit with ferromagnetic leads. This setup does not rely on any specific band structure and can therefore be realized with many different types of nanoconductors. In this talk, we will discuss its implementation with carbon nanotubes. We can reach the strong coupling limit between the electron spin and a superconducting photon cavity, with experimentally realistic parameters compatible with a slow enough decoherence of the spin quantum state. This allows us to envision the use of circuit cavity quantum electrodynamics methods for single spin manipulation and readout.
We propose theoretically a scheme for implementing a spin quantum bit in a quantum dot circuit with ferromagnetic leads. This setup does not rely on any specific band structure and can therefore be realized with many different types of nanoconductors. In this talk, we will discuss its implementation with carbon nanotubes. We can reach the strong coupling limit between the electron spin and a superconducting photon cavity, with experimentally realistic parameters compatible with a slow enough decoherence of the spin quantum state. This allows us to envision the use of circuit cavity quantum electrodynamics methods for single spin manipulation and readout.
We theoretically propose a scheme for a spin quantum bit based on a double quantum dot contacted to ferromagnetic elements. Interface exchange effects enable an all electric manipulation of the spin and a switchable strong coupling to a superconducting coplanar waveguide cavity. Our setup does not rely on any specific band structure and can in principle be realized with many different types of nanoconductors. This allows us to envision on-chip single spin manipulation and readout using cavity QED techniques.
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
The manipulation of the electronic spin degree of freedom is an important goal in the context of the development of quantum information and spin electronics. Coherent conductors connected to ferromagnetic contacts are particularly interesting in this context. Indeed, they are subject to spin-dependent quantum interferences, which can be used to manipulate the spin degree of freedom. In this talk, I will focus on effective fields induced inside a coherent conductor by a ferromagnetic contact. I will first discuss the nature of these fields. Second, I will show that these effective fields can be used to design a spin quantum bit adapted for Circuit Quantum Electrodynamics experiments[1]. This setup is based on a double quantum dot connected to two non-collinear ferromagnetic contacts. This allows to obtain a strong spin/photon coupling, which can be switched on and off with a simple gate voltage. Third, I will show that the contact-induced effective fields can also be used to induce unconventional superconducting correlations inside a normal metal wire[2]. [1] A. Cottet and T. Kontos, Phys. Rev. Lett. 105, 160502 (2010) [2] A. Cottet, unpublished
Abstract Spins confined in quantum dots are considered as a promising platform for quantum information processing. While many advanced quantum operations have been demonstrated, experimental as well as theoretical efforts are now focusing on the development of scalable spin quantum bit architectures. One particularly promising method relies on the coupling of spin quantum bits to microwave cavity photons. This would enable the coupling of distant spins via the exchange of virtual photons for two qubit gate applications, which still remains to be demonstrated with spin qubits. Here, we use a circuit QED spin–photon interface to drive a single electronic spin in a carbon nanotube-based double quantum dot using cavity photons. The microwave spectroscopy allows us to identify an electrically controlled spin transition with a decoherence rate which can be tuned to be as low as 250 kHz. We show that this value is consistent with the expected hyperfine coupling in carbon nanotubes. These coherence properties, which can be attributed to the use of pristine carbon nanotubes stapled inside the cavity, should enable coherent spin–spin interaction via cavity photons and compare favorably to the ones recently demonstrated in Si-based circuit QED experiments. Our clean and controlled nano-assembly technique of carbon nanotubes in the cavity could be further improved by purified 12 C growth to get rid of the nuclear spins resulting in an even higher spin coherence.
Coupling on-chip microwave cavities to superconducting microcircuits has provided a new platform to study the light/matter interaction at the most elementary level. Generalizing such a coupling 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 aspects of the effect of a double quantum dot on cavity photons. I will discuss the case of normal, ferromagnetic and superconducting reservoirs. In particular, the coupling of a Cooper pair splitter with cavity photons will be discussed
This thesis investigates experimentally the coupling mechanism of the charge and spin degrees of freedom in double quantum dots to high finesse superconducting microwave cavities. We use carbon nanotubes as a coherent conductor to host our quantum dots.We conceived an experimental setup and developed new fabrication methods in order to achieve control over these devices. With these methods, we scrutinize the resonant coupling of the dot's charge electronic transitions to a microwave cavity. We drive the system out of equilibrium to characterise its dynamics and extract its relevant intrinsic parameters. We examine a possible coupling of single photons to a single electron spin, using non-collinear exchange fields induced from ferromagnetic interfaces as a key ingredient to engineer this coupling. The preliminary results in this circuit architecture are promising for future spin-based QED experiments with single spins.