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PhD subjects

5 sujets IRAMIS

Dernière mise à jour : 17-09-2019


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• Mesoscopic physics

 

Towards hybrid quantum computing: from superconducting circuits to nuclear spins

SL-DRF-19-0529

Research field : Mesoscopic physics
Location :

Service de Physique de l'Etat Condensé

Groupe Quantronique

Saclay

Contact :

Emmanuel FLURIN

Daniel ESTEVE

Starting date : 01-09-2019

Contact :

Emmanuel FLURIN
CEA - DRF/IRAMIS/SPEC/GQ

0622623862

Thesis supervisor :

Daniel ESTEVE
CEA - DSM/IRAMIS/SPEC/GQ

0169085529

Personal web page : http://iramis.cea.fr/spec/Phocea/Membres/Annuaire/index.php?uid=eflurin

Laboratory link : http://iramis.cea.fr/spec/GQ/

Quantum information has emerged in past decades as a new pillar of science at the crossroad between quantum physics and information processing. In particular, quantum computation holds great promise for surpassing conventional computing at solving certain class of hard problems such as factoring large integers, searching in an unstructured database, or more realistically classifying sets, or addressing the many body problem in quantum chemistry, complex materials or nuclear physics. Quantum bits are the fundamental carriers of quantum information, and numerous condensed matter system have been shown to host degrees of freedom able to faithfully retain such quantum information, in particular in superconducting electrical oscillators or single crystalline defects in high quality materials. The PhD thesis is part of a long term research project of the Quantronics group that aims at combining precisely these two types of quantum systems in a hybrid structure: impurities trapped in solids would form high fidelity memory elements in superconducting quantum processors.

The goal of the PhD thesis will be first to optimize the coupling between the circuit and a single spin trapped in diamond and second to successfully detect the unique microwave photon generated by the de-excitation of the electron spin. This single photon will be captured by a superconducting qubit of the transmon type, a key element of the superconducting quantum processor, thus laying the foundations for a new quantum processor architecture.
Hybrid quantum circuits coupling a single spin to a superconducting resonator

SL-DRF-19-0559

Research field : Mesoscopic physics
Location :

Service de Physique de l'Etat Condensé

Groupe Quantronique

Saclay

Contact :

Denis VION

Starting date : 01-05-2019

Contact :

Denis VION
CEA - DRF/IRAMIS/SPEC/GQ

2 5529

Thesis supervisor :

Denis VION
CEA - DRF/IRAMIS/SPEC/GQ

2 5529

This PhD thesis, in cotutelle with the Institut Quantque of the University of Sherbrooke, aims at detecting a single spin with a superconducting resonator, in two distinct cases: a qubit based on a single electron in a quantum dot on the one hand, and a single NV centre spin in diamond in the second hand.

In the first case, while the spin qubit is currently viewed as a prime candidate for quantum information processing, the currently preferred readout method is destructive. The proposed research project aims at experimentally demonstrating in The Unversity of Sherbrooke a new type of measurement based on the parametric modulation of the longitudinal coupling between a superconducting microwave resonator and the qubit.

In the second case of the NV centre, its purely inductive detection with a low impedance resonator will be developed at CEA-Paris-Saclay university.
Microwave photon detector for single spin detection

SL-DRF-19-1030

Research field : Mesoscopic physics
Location :

Service de Physique de l'Etat Condensé

Groupe Quantronique

Saclay

Contact :

Patrice BERTET

Denis VION

Starting date : 01-09-2019

Contact :

Patrice BERTET
CEA - DRF/IRAMIS

0169085529

Thesis supervisor :

Denis VION
CEA - DRF/IRAMIS/SPEC/GQ

2 5529

Personal web page : http://iramis.cea.fr/spec/Phocea/Pisp/index.php?nom=patrice.bertet

Laboratory link : http://iramis.cea.fr/spec/Pres/Quantro/static/index.html

Entangling two remote quantum systems that never interact directly is an essential primitive in quantum information science and forms the basis for the modular architecture of quantum computing. When protocols to generate these remote entangled pairs rely on using traveling single-photon states as carriers of quantum information, they can be made robust to photon losses. Today, these photon based protocols are routinely implemented in the optical domain relying on high-performance photon detectors. Transposing such protocols in the microwave domain would enable quantum information processing architecture where various moderate scale quantum computation modules are linked by lossy transmission lines on which entanglement is distributed. This quantum network architecture is one of the proposals for large scale quantum computing even if it has been so far hindered by the unavailability of low-dark count photon detectors in the microwave domain. Indeed, microwave photons have energies 5 orders of magnitude lower than optical photons, and are therefore ineffective at triggering measurable phenomena at macroscopic scales. This thesis is part of a long term research project of the Quantronics group that aims at remotely combine superconducting electrical oscillators and single crystalline defects in high quality materials in a modular architecture. The PhD thesis will aim at studying and developing high performance photon detectors based on superconducting circuits in order to provide the first demonstration of remote entanglement of a single crystalline defect with a superconducting qubit
Quantum heat transport in graphene Van der Waals heterostructures

SL-DRF-19-0966

Research field : Mesoscopic physics
Location :

Service de Physique de l'Etat Condensé

Groupe Nano-Electronique

Saclay

Contact :

François PARMENTIER

Patrice ROCHE

Starting date : 01-10-2018

Contact :

François PARMENTIER
CEA - DRF/IRAMIS/SPEC/GNE

+33169087311

Thesis supervisor :

Patrice ROCHE
CEA - DRF/IRAMIS/SPEC/GNE

0169087216

Laboratory link : http://nanoelectronics.wikidot.com/research

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).

Electron tunneling time and its fluctuations

SL-DRF-19-0504

Research field : Mesoscopic physics
Location :

Service de Physique de l'Etat Condensé

Groupe Nano-Electronique

Saclay

Contact :

Carles ALTIMIRAS

Patrice ROCHE

Starting date : 01-09-2019

Contact :

Carles ALTIMIRAS
CEA - DRF/IRAMIS/SPEC/GNE

01 69 08 55 29

Thesis supervisor :

Patrice ROCHE
CEA - DRF/IRAMIS/SPEC/GNE

0169087216

Personal web page : http://iramis.cea.fr/spec/Phocea/Membres/Annuaire/index.php?uid=caltimir

Laboratory link : http://iramis.cea.fr/spec/GNE/

More : https://nanoelectronicsgroup.com/

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 by 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 semiconducting 2D electron gases where electrostatically coupled metallic gates are used to generate the electrostatic potential barrier upon which the electrons are scattered. Moreover, we will equally use them to collect the mirror influence-charges fluctuating in response to the tunneling electrons residing within the electrostatic barrier. 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 [2] allowing us to efficiently collect the signal into a RF detection chain.



In a second step, we will perform similar measurements in experimental conditions where electron-electron interactions strongly modify the transport properties across the barrier. Notably a metal/insulator quantum phase transition is driven by such interactions when a 1D wire is interrupted by an impurity, mimicking Tomonaga-Lutinger liquid dynamics [3]. We wish to investigate this physics from the original perspective of the electron tunneling time, as put forward by a recent theoretical finding [4].



The student will participate to the radiofrequency design of the samples, to their fabrication in a clean-room environment, and to their measurement exploiting low noise measurement techniques both in the near DC and the few GHz range. He will become familiar with sub-Kelvin cryogenic techniques as well.



References:

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

[2] Rolland et al., https://arxiv.org/abs/1810.06217

[3] Anthore et al., Phys. Rev. X 8, 031075 (2018)

[4] Altimiras, Portier and Joyez, Phys. Rev. X 6, 031002 (2016)

 

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