Optical and microwave cavities

- Nanoelectromechanical devices (in collaboration with the Nano-Optics and Forces group)

Nanoelectromechanical systems can be operated as ultrasensitive mass sensors and ultrahigh frequency resonators, and can also be used to explore fundamental physical phenomena such as nonlinear damping and quantum effects in macroscopic objects. Various dissipation mechanisms are known to limit the mechanical quality factors of nanoelectromechanical systems and to induce aging due to material degradation, so there is a need for methods that can probe the motion of these systems, and the stresses within them, at the nanoscale. In the hybrid group, we are working a non-invasive local optical probe for the quantitative measurement of motion and stress within a nanoelectromechanical system based on Fizeau interferometry and Raman spectroscopy. The system consists of a multilayer graphene resonator that is clamped to a gold film on an oxidized silicon surface. The resonator and the surface both act as mirrors and therefore define an optical cavity. Fizeau interferometry provides a calibrated measurement of the motion of the resonator, while Raman spectroscopy can probe the strain within the system and allows a purely spectral detection of mechanical resonance at the nanoscale.

 
LEFT : Top : Schematics of the nanoelectromechanical device. Bottom : Evolution of the Raman spectrum characteristics as a function of applied voltage and frequency. [2] RIGHT : Strain and charge doping analysis with complementary AFM and Raman measurements. (a) Analysis of Raman G and 2D modes wavenumber correlation as a function of distance from the centre of the membrane. The color of each dot indicates the distance of the probed spot from the center of the membrane. The color distribution gives a first hint about the spatial strain distribution in the membrane : the area close to the center (dark spots) nearly superimposes with the area far from the center (bright spots) where the graphene is supported by the substrate. (b-c) Strain and doping maps extracted from a). While the doping level is rather homogeneous over the whole measured region, the strain distribution displays local variations that can be understood in terms of the topography of the membrane. (d) AFM height images. [4]

 

[1] A. Reserbat-Plantey et al., EPL 96 57001 (2011) -> doi.org/10.1209/0295-5075/96/57001
[2] A. Reserbat-Plantey et al., Nature Nanotechnology, 7, 151-155 (2012) -> doi.org/10.1038/nnano.2011.250
[3] A. Reserbat-Plantey et al., J. Opt., 15, 114010 (2013) -> doi.org/10.1088/2040-8978/15/11/114010
[4] N. Bendiab et al., J. Raman Spectrosc., Accepted on September 7, 2017

 

Contact : nedjma.bendiab@neel.cnrs.fr


 
- Graphene-based superconducting quantum circuits

Devices based on the control of quantum states will revolutionize information and communications technologies. Several implementations of the quantum bit (Qubit), i.e. the building block for systems targeting quantum-enabled functionalities, were already demonstrated. Approaches based on all-superconducting materials provide the most advanced solid-state platform to date [1] but one of their drawbacks is that they must rely on magnetic effects for control and operation, which is not an industry standard for devices and starts already to be an issue in large scale circuits. On the other hand, approaches fully based on semiconductors provide spin Qubits with long coherence times that are electrically tunable and addressable. They are very promising for large scale integration because they are based on mainstream industry technologies. But fast quantum state readout will require their co-integration with superconducting resonators.

 

 

To bridge the gap between these two approaches, we propose the integration of a gapless two-dimensional semiconductor, graphene, in the key element of superconducting quantum circuits : the Josephson junction, a weak link between two superconducting electrodes. It will create an electrically tunable Josephson element. The resulting quantum circuits will gain electrical tunability, a breakthrough for control and future integration. Several pivotal elements of quantum technologies are targeted : an electrically tunable Qubit, an electrically pumped quantum limited Josephson parametric amplifier and an electrically controlled coupler between Qubits that will be a major step for future scaling (see figure).
Graphene, which can now be grown on wafer scale while maintaining high electron mobilities, is only one atom thick and can be combined in a simple manner with mainstream technologies by using recently developed transfer techniques. This is a fundamental asset for future developments and a clear advantage compared to competing technologies based on semiconductor nanowires [2,3].

 
[1] R. Barends et al., Nature 508, 500-503 (2014)
[2] T. W. Larsen et al., Phys. Rev. Lett. 115, 127001 (2015)
[3] G. de Lange et al., Phys. Rev. Lett. 115, 127002 (2015)

 

Contact : julien.renard@neel.cnrs.fr

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