Nanoelectronics Group

Post-doc positions

We are looking for excellent and highly motivated post-doc candidateS for the following projects:

 

  • Anyons on demand (2 years contract - ANR FullyQuantum 2018):

The Nanoelectronics Group currently has an opening for a Post-Doctoral Position on our experiment on Anyonic statistics with Fractional Levitons in the Fractional Quantum Hall Effect regime.
The candidate will lead a presently running experiment on the project on abelian and non-abelian statististics using on-demand anyon sources based on levitons in the FQHE regime. Through electronic Hong Ou Mandel interferences, the time control would permit an unprecedented measurement of the quantum statistical angle of e/3 or e/5 anyons or non-abelian anyons.
References:

Nature 502, 659–663 (2013) dx.doi.org/10.1038/nature12713
Preprint: A Josephson relation for fractionally charged anyons(preprint)

contact: christian.glattli@cea.fr


  • Thermal conductance of many-body quantum Hall states of graphene (2 years contract- ERC QuaHQ, 2019):

The goal of this project is to explore quantum transport of heat in new states of matter arising in ultra-clean graphene under high magnetic fields, using ultra-sensitive electronic noise measurements. This project is funded by the European Research Council (ERC-StG-2018 805080 QUAHQ).

We have an open position (starting February 2019) for a highly talented postdoctoral collaborator, with comprehensive skills in nanofabrication (in particular van der Waals heterostructures), low noise measurements, and cryogenics.

contact: François Parmentier


  • Single-charge detection for electron quantum optics (2 years post doc)

The present state of the art is to read out electron quantum optics experiments by a measurement of the average transfer probability of electrons into output ports (i.e. current) and the current noise. This project will break new ground, developing techniques for the detection of the individual single-electron wave packet.

For levitons the project will explore the use of a single-leviton induced electron-avalanche in a graphene constriction in the QHE regime, biases near breakdown, which will be detected by a measurable noise . Presently the QHE breakdown mechanisms in high-mobility h-BN graphene is unknown. The project will advance the state of the art understanding of its mechanisms and signatures, notably its ability to detect ultra-small (≤ 1 pA) DC current or short-time current pulses (yet explored in GaAs).

contact: Preden Roulleau



PhD & Intern positions

We are looking for motivated students for the following projects:

  • Electronic quantum optics in graphene

Flying qubits research led to the recent emergence of the field of electron quantum optics, where electrons play the role of photons in quantum optic like experiments. This has recently enabledthe development of electronic quantum interferometry as well as single electron sources. As of yet, such experiments have only been successfully implemented in semi-conductor heterostructures cooled at extremely low temperatures. Realizing electron quantum optics experiments in graphene, an inexpensive material showing a high degree of quantum coherence even at moderately low temperatures, would be a strong evidence that quantum computing in graphene is within reach.

One of the most elementary building blocks necessary to perform electron quantum optics experiments is the electron beam splitter, which is the electronic analog of a beam splitter for light. However, the usual scheme for electron beam splitters in semi-conductor heterostructures isnot available in graphene because of its gapless band structure. I propose a breakthrough in this direction where pn junction plays the role of electron beam splitter. Based on this, an electronic Mach Zehnder interferometer will be studied to understand the quantum coherence properties of graphene. This PhD proposal is part of the ERC starting COHEGRAPH (2016)

contact: Preden Roulleau


  • Electron tunneling time and its fluctuations

Challenging our classical intuition, quantum tunneling has fascinated physicists for decades. Very soon after its discovery, it raised the question of how much time do particles spend under the classically forbidden barrier. Despite its simplicity, such a question is ill defined in terms of quantum observables and does not admit a single answer, thus triggering over the past decades a bunch of different definitions corresponding to different (thought) scenarios.

          Following a proposal of Büttiker & collaborators [1], we will address this question from the perspective of a well-defined observable: that is, measuring the spectrum of time fluctuations of the number of particles residing within the classically forbidden barrier. The idea is to exploit semi-conducting 2D electron gases where electrostatically coupled metallic gates not only can be used to generate the electrostatic potential barrier upon which the electrons are scattered (a Quantum Point Contact), but could be used as well to collect the mirror influence-charges fluctuating in response to the tunneling electrons residing beneath the gate. Despite its conceptual simplicity, implementing such a scenario is a formidable task since it demands collecting a tiny radiofrequency (RF) signal emitted by a huge output-impedance source in a sub-Kelvin (dilution) refrigerator. We will build upon the group’s expertise in RF design and ultra-low noise measurements in cryogenic environments in order to overcome this challenge, notably implementing recently developed high impedance RF matching circuits allowing us to efficiently collect the signal into a RF detection chain.

[1] Pedersen, van Langen, and Büttiker, Phys. Rev. B 57, 1838 (1998).

contact: Carles Altimiras


  • Stabilization of a Fock state in a dc biased Josephson junction circuit

This project belongs to the fast growing field of quantum microwaves with Josephson junction circuits. We wish to show that by astutely designing the electromagnetic environment of a dc biased Josephson junction, one can stabilize a Fock state of a microwave resonator. The device involved in this project consists in a Josephson junction coupled to two resonators of different frequencies and voltage biased. As the Josephson junction is a non-dissipative element, a DC current can flow through the circuit only if the energy provided by the generator upon the transfer of a Cooper pair is converted into electromagnetic excitations of the resonators. The purpose of this internship is to demonstrate that this device can be also used to stabilize the single photon Fock state in one of the resonators: by increasing the coupling of one resonator to the junction, one enters a regime where the transition between one and two photon states is suppressed. If the tunneling of each Cooper pair is associated to the emission of a single photon in this resonator, this blockade doesn’t stabilize the single photon Fock state, as a Cooper pair can tunnel backward via the reabsorption of the photon. To suppress this process, we will use the second mode as a dump with a very short lifetime of the dump. The voltage will be set so that the tunneling of a Cooper pair is associated to the emission of a photon in the two modes, the dump modes empties quickly, so that the back tunneling of a Cooper pair is forbidden by energy conservation, thus stabilizing the single photon Fock state of the strongly coupled mode. The trainee will be involved in all the steps of the experiment: design and fabrication of the sample, using nanolithography, cooling of the sample by a dilution refrigerator, and characterization by ultra-low-noise microwave measurements. All these techniques are well mastered by our group.

contact: Fabien Portier


  • Quantum thermal engine with a voltage biased Josephson junction

This project belongs to the fast growing field of quantum thermodynamics. We wish to develop a simple thermal engine whose operating behavior is intrinsically quantum. The device involved in this project consists in a Josephson junction coupled to two resonators of different frequencies and voltage biased. As the Josephson junction is a non-dissipative element, a DC current can flow through the circuit only if the energy provided by the generator upon the transfer of a Cooper pair is converted into electromagnetic excitations of the resonators. We have recently proven that the corresponding radiation is not classical when the tunneling of each Cooper pair is associated to the emission of a photon in both resonators[1]. The purpose of this internship is to demonstrate that this device can be used as a thermal engine, when the two modes are at held at different temperatures, the higher frequency resonator being at a higher temperature. The voltage bias is now set so that the work provided by the generator corresponds to the difference of the energies of photons in the two modes. One then expects a backflow of Cooper pairs, associated to the absorption of  photons at the higher frequency and re-emission of photons at the lower frequency, resulting in the conversion of heat into electrical work. Unlike most classical machines, the efficiency of this engine is predicted to be high, even at maximum power[2]. The sample being already available, the trainee will perform the experiment, cool the sample with a dilution refrigerator, ensure different populations of the two modes and measure the induced current by ultra low-noise measurements. All these techniques are well mastered by our group.

[1] M. Westig et al., Phys Rev Lett 119, 137001 (2017)

[2] P. P. Hofer, J.-R. Souquet, and A. A. Clerk, Phys. Rev. B 93, 041418 (2016)

contact: Fabien Portier & Carles Altimiras


  • Quantum heat transport in graphene Van der Waals heterostructures

The goal of this project is to explore quantum transport of heat in new states of matter arising in ultra-clean graphene in high magnetic fields, using ultra-sensitive electronic noise measurements.

The ability to obtain ultra-clean graphene (a two-dimensional crystal made of Carbon atoms in a honeycomb lattice) samples has recently allowed the observation of new phases of condensed matter in graphene under high magnetic fields. In particular, new states of the quantum Hall effect were observed at low charge carrier density [1], where interactions and electronic correlations can either make graphene completely electrically insulating, or give rise to the quantum spin Hall effect. In the latter, the bulk of the two-dimensional crystal is insulating, while electronic current is only carried along the edges of the crystal, with opposite spins propagating in opposite directions. The exact nature of those various states is still not fully understood, as one cannot probe the properties of the insulating regions by usual electron transport measurements.

We propose a new approach to probe those phases, based on the measurement of quantum heat flow carried by chargeless excitations such as spin waves, at very low temperature. Our method will consist in connecting the graphene crystal to small metallic electrodes which will be used as heat reservoirs. The temperature of each reservoir will be inferred by ultra-sensitive noise measurements [2], allowing us to extract the heat flow.

The first step of this project will consist in fabricating the samples made of graphene encapsulated in hexagonal boron nitride [3]. This technique, which we have recently developed in our lab, allows to obtain large-area, ultra-clean graphene flakes. In parallel, an experimental platform for low-temperature, high magnetic field, ultra-high sensitivity noise measurements will be set up.

[1] Young et al., Nature 505, 528-532 (2014).
[2] Jezouin, Parmentier et al., Science 342, 601 (2013).
[3] Wang et al., Science 342, 614 (2013).

contact: François Parmentier

 
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