Periodic Reporting for period 4 - COHEGRAPH (Electron quantum optics in Graphene)
Berichtszeitraum: 2020-11-01 bis 2022-07-31
The goal of the project is to show that graphene is a promising host material for quantum manipulation of flying qubits.
Flying qubits are mobile qubits propagating in quantum circuits.
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 is not available in graphene because of its gapless band structure.
In my ERC project, I propose a breakthrough in this direction where pn junction plays the role of electron beam splitter.
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.
Showing that quantum computing is within reach is one of the most important technological challenge of our society, supported by the European flagship.
Flying qubits are mobile qubits propagating in quantum circuits.
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 is not available in graphene because of its gapless band structure.
In my ERC project, I propose a breakthrough in this direction where pn junction plays the role of electron beam splitter.
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.
Showing that quantum computing is within reach is one of the most important technological challenge of our society, supported by the European flagship.
From the begining of the project, we first had to install a dilution refrigerator (received in July 2017) and cable the necessary DC and high frequency lines.
We can now carry out measurements at 13 Tesla with a temperature below 20mK (base temperature of the fridge 10mK).
Shot noise measurements realized on a quantum point contact (GaAs heterostructure) have confirmed an electronic temperature of 20mK.
A high frequency line (0-40 GHz) completes the set up.
The most challenging part of the project was to achieve high mobility graphene samples base on hBN encapsulation.
This has been recently achieved: we can now benefit from a dedicated platform to check the quality of the graphene sample at the different
fabrication step (this platform is composed of a Raman spectrometer, an AFM, two transfer stations and an automatized microscope).
First fabricated sample (an electronic Mach Zehnder in graphene) measured in september revealed interference oscillations with a maximum visibility of 30%.
Following the Work Package 1, next step was to control the transmission probability of the Mach Zehnder beam splitters.
A second generation of samples, with adapted side gates have been measured and have shown the expected response of the transmission probability.
Most of the technological challenges have been achieved dufring this first period. Next work packages will consist in the implementation of well know technics
in order to perform, for the first time, complex electronic quantum optics experiments in graphene.
We finally achieved a fully tunable Mach Zehnder interferometer (see WP1.1) [1]. By studying the coherence properties at finite bias, we managed to detect propagating
magnons through the interferometer (see WP1.2) [2]. Following WP1.2 we measured the interference visibiliy for interferometers of different sizes and model
decoherence effects [3,4]. As described in WP3.2 and WP3.3 we managed to implement the Leviton source and to perform Hong ou Mandel experiment.
This led to the first tomography of an itinerant electron in graphene with the computation of the Wigner function [5,6]
[1] Quantum Hall valley splitters and a tunable Mach-Zehnder interferometer in graphene, M. Jo,
P. Brasseur, A. Assouline, G. Fleury, H. -S. Sim, K. Watanabe, T. Taniguchi, W. Dumnernpanich,
P. Roche, D. C. Glattli, N. Kumada, F. D. Parmentier, and P. Roulleau, Phys. Rev.
Lett. 126, 146803 (2021) – Editor’s suggestion, Featured in Physics
[2] Excitonic nature of magnons in a quantum Hall ferromagnet, A. Assouline, M. Jo, P. Brasseur,
K. Watanabe, T. Taniguchi, Th. Jolicoeur, D. C. Glattli, N. Kumada, P. Roche, F. D. Parmentier
P. Roulleau , Nature Physics, 17, 1369 (2021)
[3] Scaling behavior of electron decoherence in a graphene Mach-Zehnder interferometer, M. Jo, June-Young M. Lee,
A. Assouline, P. Brasseur, K. Watanabe, T. Taniguchi, P. Roche, D. C. Glattli, N. Kumada, F. D. Parmentier, H. -S. Sim & P. Roulleau
Nature Communications, 13, 5473 (2022)
[4] Positioning of edge states in a quantum Hall graphene pn junction
I. M. Flór, A. Lacerda-Santos, G. Fleury, P. Roulleau, and X. Waintal
Phys. Rev. B 105, L241409 (2022)
[5,6] to be submitted
We can now carry out measurements at 13 Tesla with a temperature below 20mK (base temperature of the fridge 10mK).
Shot noise measurements realized on a quantum point contact (GaAs heterostructure) have confirmed an electronic temperature of 20mK.
A high frequency line (0-40 GHz) completes the set up.
The most challenging part of the project was to achieve high mobility graphene samples base on hBN encapsulation.
This has been recently achieved: we can now benefit from a dedicated platform to check the quality of the graphene sample at the different
fabrication step (this platform is composed of a Raman spectrometer, an AFM, two transfer stations and an automatized microscope).
First fabricated sample (an electronic Mach Zehnder in graphene) measured in september revealed interference oscillations with a maximum visibility of 30%.
Following the Work Package 1, next step was to control the transmission probability of the Mach Zehnder beam splitters.
A second generation of samples, with adapted side gates have been measured and have shown the expected response of the transmission probability.
Most of the technological challenges have been achieved dufring this first period. Next work packages will consist in the implementation of well know technics
in order to perform, for the first time, complex electronic quantum optics experiments in graphene.
We finally achieved a fully tunable Mach Zehnder interferometer (see WP1.1) [1]. By studying the coherence properties at finite bias, we managed to detect propagating
magnons through the interferometer (see WP1.2) [2]. Following WP1.2 we measured the interference visibiliy for interferometers of different sizes and model
decoherence effects [3,4]. As described in WP3.2 and WP3.3 we managed to implement the Leviton source and to perform Hong ou Mandel experiment.
This led to the first tomography of an itinerant electron in graphene with the computation of the Wigner function [5,6]
[1] Quantum Hall valley splitters and a tunable Mach-Zehnder interferometer in graphene, M. Jo,
P. Brasseur, A. Assouline, G. Fleury, H. -S. Sim, K. Watanabe, T. Taniguchi, W. Dumnernpanich,
P. Roche, D. C. Glattli, N. Kumada, F. D. Parmentier, and P. Roulleau, Phys. Rev.
Lett. 126, 146803 (2021) – Editor’s suggestion, Featured in Physics
[2] Excitonic nature of magnons in a quantum Hall ferromagnet, A. Assouline, M. Jo, P. Brasseur,
K. Watanabe, T. Taniguchi, Th. Jolicoeur, D. C. Glattli, N. Kumada, P. Roche, F. D. Parmentier
P. Roulleau , Nature Physics, 17, 1369 (2021)
[3] Scaling behavior of electron decoherence in a graphene Mach-Zehnder interferometer, M. Jo, June-Young M. Lee,
A. Assouline, P. Brasseur, K. Watanabe, T. Taniguchi, P. Roche, D. C. Glattli, N. Kumada, F. D. Parmentier, H. -S. Sim & P. Roulleau
Nature Communications, 13, 5473 (2022)
[4] Positioning of edge states in a quantum Hall graphene pn junction
I. M. Flór, A. Lacerda-Santos, G. Fleury, P. Roulleau, and X. Waintal
Phys. Rev. B 105, L241409 (2022)
[5,6] to be submitted
_ First tunable tunable Mach Zehnder interferometer [1]
_ First observation of the dipole moment of magnons in a quantum Hall ferromagnet [2]
_ First measurment of the coherence lenght in graphene [3]
_ First single electron source (Levitons' protocol) in graphene [5]
_ First tomography and Wigner function of a Leviton [6]
[1] Quantum Hall valley splitters and a tunable Mach-Zehnder interferometer in graphene, M. Jo,
P. Brasseur, A. Assouline, G. Fleury, H. -S. Sim, K. Watanabe, T. Taniguchi, W. Dumnernpanich,
P. Roche, D. C. Glattli, N. Kumada, F. D. Parmentier, and P. Roulleau, Phys. Rev.
Lett. 126, 146803 (2021) – Editor’s suggestion, Featured in Physics
[2] Excitonic nature of magnons in a quantum Hall ferromagnet, A. Assouline, M. Jo, P. Brasseur,
K. Watanabe, T. Taniguchi, Th. Jolicoeur, D. C. Glattli, N. Kumada, P. Roche, F. D. Parmentier
P. Roulleau , Nature Physics, 17, 1369 (2021)
[3] Scaling behavior of electron decoherence in a graphene Mach-Zehnder interferometer, M. Jo, June-Young M. Lee,
A. Assouline, P. Brasseur, K. Watanabe, T. Taniguchi, P. Roche, D. C. Glattli, N. Kumada, F. D. Parmentier, H. -S. Sim & P. Roulleau
Nature Communications, 13, 5473 (2022)
[4] Positioning of edge states in a quantum Hall graphene pn junction
I. M. Flór, A. Lacerda-Santos, G. Fleury, P. Roulleau, and X. Waintal
Phys. Rev. B 105, L241409 (2022)
[5,6] to be submitted
_ First observation of the dipole moment of magnons in a quantum Hall ferromagnet [2]
_ First measurment of the coherence lenght in graphene [3]
_ First single electron source (Levitons' protocol) in graphene [5]
_ First tomography and Wigner function of a Leviton [6]
[1] Quantum Hall valley splitters and a tunable Mach-Zehnder interferometer in graphene, M. Jo,
P. Brasseur, A. Assouline, G. Fleury, H. -S. Sim, K. Watanabe, T. Taniguchi, W. Dumnernpanich,
P. Roche, D. C. Glattli, N. Kumada, F. D. Parmentier, and P. Roulleau, Phys. Rev.
Lett. 126, 146803 (2021) – Editor’s suggestion, Featured in Physics
[2] Excitonic nature of magnons in a quantum Hall ferromagnet, A. Assouline, M. Jo, P. Brasseur,
K. Watanabe, T. Taniguchi, Th. Jolicoeur, D. C. Glattli, N. Kumada, P. Roche, F. D. Parmentier
P. Roulleau , Nature Physics, 17, 1369 (2021)
[3] Scaling behavior of electron decoherence in a graphene Mach-Zehnder interferometer, M. Jo, June-Young M. Lee,
A. Assouline, P. Brasseur, K. Watanabe, T. Taniguchi, P. Roche, D. C. Glattli, N. Kumada, F. D. Parmentier, H. -S. Sim & P. Roulleau
Nature Communications, 13, 5473 (2022)
[4] Positioning of edge states in a quantum Hall graphene pn junction
I. M. Flór, A. Lacerda-Santos, G. Fleury, P. Roulleau, and X. Waintal
Phys. Rev. B 105, L241409 (2022)
[5,6] to be submitted