Tunable nonadiabatic excitation in a single-electron quantum dot.

National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom.
Physical Review Letters (Impact Factor: 7.94). 03/2011; 106(12):126801. DOI: 10.1103/PhysRevLett.106.126801
Source: PubMed

ABSTRACT We report the observation of nonadiabatic excitations of single electrons in a quantum dot. Using a tunable-barrier single-electron pump, we have developed a way of reading out the excitation spectrum and level population of the dot by using the pump current as a probe. When the potential well is deformed at subnanosecond time scales, electrons are excited to higher levels. In the presence of a perpendicular magnetic field, the excited states follow a Fock-Darwin spectrum. Our experiments provide a simple model system to study nonadiabatic processes of quantum particles.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the evolution of a single-electron packet of Lorentzian shape along an edge of the integer quantum Hall regime or in a Mach-Zehnder interferometer, considering a capacitive Coulomb interaction and using a bosonization approach. When the packet propagates along a chiral quantum Hall edge, we find that its electron density profile becomes more distorted from Lorentzian due to the generation of electron-hole excitations, as the interaction strength increases yet stays in a weak interaction regime. However, as the interaction strength becomes larger and enters a strong interaction regime, the distortion becomes weaker and eventually the Lorentzian packet shape is recovered. The recovery of the packet shape leads to an interesting feature of the interference visibility of the symmetric Mach-Zehnder interferometer whose two arms have the same interaction strength. As the interaction strength increases, the visibility decreases from the maximum value in the weak interaction regime, and then increases to the maximum value in the strong interaction regime. We argue that this counterintuitive result also occurs under other types of interactions.
    Physical review. B, Condensed matter 04/2013; 86(23). · 3.77 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate adiabatic and non-adiabatic emission of single particles into an edge state using an analytically solvable dynamical scattering matrix model of an on-demand source. We compare adiabatic and non-adiabatic emissions by considering two geometries: a collider geometry where two emitters are coupled to two different edge states and a series geometry where two emitters are coupled to the same edge state. Most effects observed for adiabatic emitters also occur for non-adiabatic emitters. In particular this applies to effects arising due to the overlap of wave-packets colliding at a quantum point contact. Specifically we compare the Pauli peak (the fermionic analog of the bosonic Hong-Ou-Mandel dip) for the adiabatic and non-adiabatic collider and find them to be similar. In contrast we find a striking difference between the two operating conditions in the series geometry in which particles are emitted into the same edge state. Whereas the squared average charge current can be nullified for both operating conditions, the heat current can be made to vanish only with adiabatic emitters.
    Physical Review B 03/2013; 87(12):125429. · 3.77 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: I analyze the correlation function of currents generated by the periodically driven quantum capacitor emitting single electrons and holes into the chiral waveguide. I compare adiabatic and non-adiabatic, transient working regimes of a single-electron emitter and find the striking difference between the correlation functions in two regimes. Quite generally for the system driven with frequency $\Omega$ the correlation function depends on two frequencies, $\omega$ and $\ell \Omega - \omega$, where $\ell$ is an integer. For the emitter driven non-adiabatically the correlation functions for different $\ell$ are similar and almost symmetric in $\omega$. While in the case of adiabatic drive the correlation functions for $\ell \ne 0$ are highly asymmetric in $\omega$ and exceed significantly the one corresponding to $\ell = 0$. Under optimal operating conditions the correlation function for odd $\ell$ is zero.
    Physical Review B 04/2013; 88(3). · 3.77 Impact Factor