Abstract
The quantum coherence of electronic quasiparticles underpins many of the emerging transport properties of conductors at small scales. Novel electronic implementations of quantum optics devices are now available with perspectives such as 'flying' qubit manipulations. However, electronic quantum interferences in conductors remained up to now limited to propagation paths shorter than $30\,\mu$m, independently of the material. Here we demonstrate strong electronic quantum interferences after a propagation along two $0.1\,$mm long pathways in a circuit. Interferences of visibility as high as $80\%$ and $40\%$ are observed on electronic analogues of the Mach-Zehnder interferometer of, respectively, $24\,\mu$m and $0.1\,$mm arm length, consistently corresponding to a $0.25\,$mm electronic phase coherence length. While such devices perform best in the integer quantum Hall regime at filling factor 2, the electronic interferences are restricted by the Coulomb interaction between copropagating edge channels. We overcome this limitation by closing the inner channel in micron-scale loops of frozen internal degrees of freedom, combined with a loop-closing strategy providing an essential isolation from the environment.
Highlights
Ballistic electrons allow for advanced quantum manipulations at the single-electron level in circuits, in the spirit of the manipulation of photons in quantum optics [1,2,3]
While such devices perform best in the integer quantum Hall regime at filling factor 2, the electronic interferences are restricted by the Coulomb interaction between copropagating edge channels
We demonstrate that the electron quantum coherence in solid-state circuits can be extended to the macroscopic scale by strongly suppressing through circuit nanoengineering the dominant decoherence mechanism
Summary
Ballistic electrons allow for advanced quantum manipulations at the single-electron level in circuits, in the spirit of the manipulation of photons in quantum optics [1,2,3]. Perspectives notably include a different paradigm for quantum-information processing with a nonlocal architecture based on “flying-qubits” encoded, for example, by the presence or absence of an electron within a propagating wave packet [1,2,4,5,6,7]. The emblematic chiral edge channels propagating along a two-dimensional (2D) conductor in the quantum Hall regime are generally considered ideal 1D conductors. Their analogy with light beams, their in situ tunability by field effect, and the availability of single-electron emitters were exploited to implement the electronic analogues of optical devices, such as the interferometers of types Fabry-Perot [8], Mach-Zehnder [9], Hanbury-Brown and Twiss [10], and Hong-Ou-Mandel [11].
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