D. C. Glattli

Minimal-excitation states for electron quantum optics using levitons

The on-demand generation of pure quantum excitations is important for the operation of quantum systems, but it is particularly difficult for a system of fermions. This is because any perturbation affects all states below the Fermi energy, resulting in a complex superposition of particle and hole excitations. However, it was predicted nearly 20 years ago that a Lorentzian time-dependent potential with quantized flux generates a minimal excitation with only one particle and no hole. Here we report that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact. Partitioning the excitations with an electronic beam splitter generates a current noise that we use to measure their number. Minimal-excitation states are observed for Lorentzian pulses, whereas for other pulse shapes there are significant contributions from holes. Further identification of levitons is provided in the energy domain with shot-noise spectroscopy, and in the time domain with electronic Hong–Ou–Mandel noise correlations. The latter, obtained by colliding synchronized levitons on a beam splitter, exemplifies the potential use of levitons for quantum information: using linear electron quantum optics in ballistic conductors, it is possible to imagine flying-qubit operation in which the Fermi statistics are exploited to entangle synchronized electrons emitted by distinct sources. Compared with electron sources based on quantum dots, the generation of levitons does not require delicate nanolithography, considerably simplifying the circuitry for scalability. Levitons are not limited to carrying a single charge, and so in a broader context n-particle levitons could find application in the study of full electron counting statistics. But they can also carry a fraction of charge if they are implemented in Luttinger liquids or in fractional quantum Hall edge channels; this allows the study of Abelian and non-Abelian quasiparticles in the time domain. Finally, the generation technique could be applied to cold atomic gases, leading to the possibility of atomic levitons.

Observation of the e/3 Fractionally Charged Laughlin Quasiparticle

The existence of fractional charges carrying current is experimentally demonstrated. Using a 2D electron system in a high perpendicular magnetic field we measure the shot noise associated with tunneling in the fractional quantum Hall regime at Landau level filling factor 1/3. The noise gives a direct determination of the quasiparticle charge, which is found to be

An On-Demand Coherent Single Electron Source

{e}^{*}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}e/3

Determination of the intershell conductance in multiwalled carbon nanotubes.

as predicted by Laughlin. The existence of

Violation of Kirchhoff's Laws for a Coherent RC Circuit

e/3

Four-Point Resistance of Individual Single-Wall Carbon Nanotubes

Laughlin quasiparticles is unambiguously confirmed by the shot noise to Johnson-Nyquist noise crossover found for temperature

Geometrical dependence of high-bias current in multiwalled carbon nanotubes.

\ensuremath{\Theta}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}e}^{*}{V}_{\mathrm{ds}}/{2k}_{B}

Evidence for Luttinger-Liquid Behavior in Crossed Metallic Single-Wall Nanotubes

.

Electron quantum optics: partitioning electrons one by one.

We report on the electron analog of the single-photon gun. On-demand single-electron injection in a quantum conductor was obtained using a quantum dot connected to the conductor via a tunnel barrier. Electron emission was triggered by the application of a potential step that compensated for the dot-charging energy. Depending on the barrier transparency, the quantum emission time ranged from 0.1 to 10 nanoseconds. The single-electron source should prove useful for the use of quantum bits in ballistic conductors. Additionally, periodic sequences of single-electron emission and absorption generate a quantized alternating current.

Quantum tomography of an electron

We report on the intershell electron transport in multiwalled carbon nanotubes (MWNTs). To do this, local and nonlocal four-point measurements are used to study the current path through the different shells of a MWNT. For short electrode separations less, similar 1 mum the current mainly flows through the two outer shells, described by a resistive transmission line with an intershell conductance per length of approximately (10 kOmega)(-1)/microm. The intershell transport is tunnel type and the transmission is consistent with the estimate based on the overlap between pi orbitals of neighboring shells.