💥 Control of a flying qubit in graphene

2024-02-22 05:00:06

A collaboration of researchers around SPEC Nanoelectronics group takes an important step forward by controlling for the first time a quantum superposition of electronic flying qubits. A flying qubit is a non-localized quantum bit (or qubit) that can be manipulated during its propagation. If the development of flying qubits carried by photons has already been achieved, the contrôle (The word control can have several meanings. It can be used as a synonym for examination,…) The complete model of a flying qubit carried by an electronic wave in a solid remained to be demonstrated.

Flying qubit based on pn junction. The blue (n side) and red (p side) lines highlight the conduction channels at the edge of the graphene substrate. It is shown that the superposition (In quantum mechanics, the superposition principle states that the same quantum state can…) quantum of the leviton states, at the level of the conduction channel between the sides n (light blue) and p (pink) is perfectly controlled.

In this innovative work, it is shown that it is possible to control the quantum superposition of individual electronic pulses, propagating in an interferometer formed by a graphene pn junction. This achievement marks an important step forward toward the on-demand generation of entangled quantum pairs, a requirement for connecting remote quantum computers.

The principle of a qubit carried by a solid substrate, such as a superconducting qubit or a semiconductor quantum dot, is based on a fixed and localized system at two levels. In contrast, “flying” qubits carried by an electronic current (ie an electronic wave) which propagates, offer the advantage of being able to be generated on demand and to be able to be manipulated during their propagation. The hardware support simply contains a architecture (Architecture can be defined as the art of building buildings.) expandable logic gates.

One of the most studied techniques involves manipulating the electronic states of a high-mobility gallium arsenide (GaAs) semiconductor using an interferome. Be Mach-Zehnder type electronic. The realization of the interferometer requires an electron beam splitter, one-dimensional conduction channels with low dissipation and a source ofelectron (The electron is an elementary particle of the lepton family, and has a charge…) unique, which we know how to develop. The interference obtained is, however, too sensitive to heat, fluctuations in electrical voltage andenergy (In the common sense, energy designates everything that allows us to carry out work, make energy, etc.) injected electrons, to allow the creation of an electron flying qubit in this configuration.

The challenge was met by constructing an electronic Mach-Zehnder interferometer based on a graphene pn junction and coupled to a source of unique electrons called e “let’s levitate*”. The graphene sample is simply deposited in a well-controlled manner on an insulating substrate. The application of a magnetic field (In physics, the magnetic field (or magnetic induction, or flux density…) external to the system induces the formation of one-dimensional conduction channels on either side of the junction (La Jonction is a district of the city of Geneva (Switzerland), its colloquial name is “la Jonquille”) pn (see figure). The entry and exit points at the pn junction are thus clearly defined and act as electron beam splitters, forming a Mach-Zehnder interferometer. Compared to conventional GaAs-based interferometers, the interferometer produced has ten times greater noise tolerance thermal (Thermal is the science which deals with the production of energy, the use of…) or tension [1,2].

With this device, the operation of a flying electron qubit might be obtained by manipulating the superposition of quantum states |0> and |1> of a leviton, respectively defined by the Electronic states in the conduction channel on the sidesn and p. It is notably shown that the polar angle (θ), for which tan(θ) is the amplitude ratio between the two superimposed states |1> and |0>, can be controlled © by adjusting the transmission of the beam splitter at the input of the pn junction (Fig. 1). At the same time, the relative phase Aharonov Bohm (Ï•) between |0> and |1>, induced by the presence of the field B, can be adjusted according to the value of this external magnetic field. Complete control of the two phases θ and Ï• makes it possible to obtain the desired superposition state [3].

This demonstration of perfect control of a flying electronic qubit is an important step forward for designing a solid-state device enabling quantum information transfer. It should now be possible to generate entangled flying qubit pairs on demand from operations on two-electron flying qubits. Another way of research (Scientific research refers primarily to all actions undertaken with a view to…)requiring a new technological effort: shortening the impulse of the levitons, in order to allow a multiplexing (Multiplexing is a technique which consists of passing two or more pieces of information to…) temporal.

Note

* A leviton is the injection of a single electron in the form of a Lorentzian pulse, avoiding any parasitic excitation of other electrons in the system.

References

[1] “Quantum hall valley splitters and a tunable Mach-zehnder interferometer in graphene”,
Jo, M Jo, P Brasseur, Assouline A, Fleury G, Sim HS, Watanabe K, Taniguchi T, Dumnernpanich W, Roche P, Glattli DC, Kumada N, Parmentier FD, Roulleau P, Physical Review Letters 126(14) (2021) 146803.

[2] “Scaling behavior of electron decoherence in a graphene Mach-Zehnder interferometer”,
M Jo, JYM Lee, A Assouline, P Brasseur, K Watanabe, T Taniguchi, P Roche, DC Glattli, N Kumada, Parmentier FD, Sim HS, Roulleau P, Nature Communications 13(1), (2022) 5473.

[3] “Emission and coherent control of Levitons in graphene”,
Assouline, Pugliese, Chakraborty, Seunghun Lee, Bernabeu, Jo, Watanabe, Taniguchi, DC Glattli, Kumada, Sim, FD, Parmentier, P Roulleau, Science 382(6676) (2023) 1260-1264.

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