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Quantum Circuits & Matter (QCMX)

QCMX members
 

Jean-Damien Pillet
(Maître de Conférences, École polytechnique)

jean-damien.pillet[at]polytechnique.edu

Building 83, Salle 83-20-20
Phone: +33169334476

Landry Bretheau
(Maître de Conférences, École polytechnique)

landry.bretheau[at]polytechnique.edu

Building 83, Salle 83-20-20
Phone: +33169334477


Landry (left) and Jean-Damien (right)
proud of their brand new He3 cylinder


QCMX activity

The purpose of QCMX's activity is to explore the quantum properties of electronic circuits and matter. The strategy consists in coupling superconducting circuits normally used to process quantum information to materials in order to probe their quantum properties and discover new electronic states of matter. This could make it possible to identify new carriers of quantum information and to simulate complex many-body quantum problems.


A laboratory dedicated to quantum circuits

In September 2017, a new activity dedicated to the development of new quantum technologies was created within l'X. QCMX members are currently building a space which will allow the realization and the manipulation of hybrid quantum circuits with access to temperatures close to absolute zero (some mK), equipment in the microwave range for quantum control and nanofabrication tools for the creation of new architectures. At the end of 2018, the coldest point of l'X will fall below 10mK thanks to the arrival of its first dilution cryostat (from the company BlueFors) in the QCMX laboratory, then already equipped to allow in 2019 the coherent measurement of the first quantum circuit of the École polytechnique.

 

One of the crucial ingredients for the operation of quantum circuits is the non-linearity provided by a non-dissipative electronic component called a Josephson junction. These junctions are usually made of two superconductors coupled by tunnel effect through a thin insulating barrier. There is however a wider class of Josephson junctions where superconductors are connected by quantum conductors, such as graphene, semiconductor nanowires or carbon nanotubes. In these systems, barely exploited in the context of quantum circuits, physics is richer because they host additional degrees of freedom associated with the electronic properties of quantum conductors. The purpose of the QCMX laboratory is to use this unexploited resource to design new quantum devices, notably through the development of ultra-clean growth of carbon nanotubes that can be integrated into superconducting circuits.

Such Josephson junctions then host elementary electronic excitations in the GHz energy range that can be controlled coherently by means of microwave signals. Our circuits, placed in a microwave cavity to protect it from environmental decoherence, will allow to detect new electronic states of matter such as, for example, Andreev Bound States, Weyl fermions or Majorana fermions.


Quantum simulations

Hybrid quantum circuit architectures as developed within the QCMX activity offer tremendous opportunities for quantum simulation, particularly to answer modern questions of fundamental Physics.

For example, a charge trapped in a nanotube or a semiconducting nanowire, connected in parallel to a Josephson junction can simulate the problem of a spin 1/2 immersed in a space-dependent magnetic field. In the quantum regime, the degrees of freedom of spin and position are entangled and obey a joined dynamic of great complexity. This experiment would make it possible to understand in more details the spin-boson model which is at the heart of the description of the dissipation in quantum physics.

Beyond this basic situation, it is possible to imagine more complex systems based on networks of several quantum objects. For example, a carbon nanotube connected to multiple superconducting electrodes may behave as a network of quantum dots. QCMX members are currently developing strategies to perform the quantum teleportation of an electron within such electronic device.


Positions

We are looking for a postdoc to work for two years on the project Quantum Information Processing with Hybrid Quantum Circuit (QIPHSC).


With the financial support of Ecole Polytechnique (start-up grant QCMX), Agence Nationale de la Recherche (grant ANR-18-CE47-0012 JCJC QIPHSC) and DIM Ile-de-France SIRTEQ (grant ONQC).