43 research outputs found
Isolated Ballistic Non-Abelian Interface Channel
Non-abelian anyons are prospective candidates for fault-tolerant topological
quantum computation due to their long-range entanglement. Curiously these
quasiparticles are charge-neutral, hence elusive to most conventional
measurement techniques. A proposed host of such quasiparticles is the =5/2
quantum Hall state. The gapless edge modes can provide the topological order of
the state, which in turn identifies the chirality of the non-abelian mode.
Since the =5/2 state hosts a variety of edge modes (integer, fractional,
neutral), a robust technique is needed to isolate the fractional channel while
retaining its original non-abelian character. Moreover, a single non-abelian
channel can be easily manipulated to interfere, thus revealing the state's
immunity to decoherence. In this work, we exploit a novel approach to gap-out
the integer modes of the =5/2 state by interfacing the state with integer
states, =2 & =3 (1). The electrical conductance of the isolated
interface channel was 0.5e/h, as expected. More importantly, we find a
thermal conductance of 0.5T (with =/3h),
confirming unambiguously the non-abelian nature of the =1/2 interface
channel and its Particle-Hole Pfaffian topological order. Our result opens new
avenues to manipulate and test other exotic QHE states and braid, via
interference, the isolated fractional channels.Comment: 20 pages, 4 main figure
Controlled Dephasing of a Quantum Dot: From Coherent to Sequential Tunneling
Resonant tunneling through identical potential barriers is a textbook problem
in quantum mechanics. Its solution yields total transparency (100% tunneling)
at discrete energies. This dramatic phenomenon results from coherent
interference among many trajectories, and it is the basis of transport through
periodic structures. Resonant tunneling of electrons is commonly seen in
semiconducting 'quantum dots'. Here we demonstrate that detecting
(distinguishing) electron trajectories in a quantum dot (QD) renders the QD
nearly insulating. We couple trajectories in the QD to a 'detector' by
employing edge channels in the integer quantum Hall regime. That is, we couple
electrons tunneling through an inner channel to electrons in the neighboring
outer, 'detector' channel. A small bias applied to the detector channel
suffices to dephase (quench) the resonant tunneling completely. We derive a
formula for dephasing that agrees well with our data and implies that just a
few electrons passing through the detector channel suffice to dephase the QD
completely. This basic experiment shows how path detection in a QD induces a
transition from delocalization (due to coherent tunneling) to localization
(sequential tunneling)
Electron Pairing of Interfering Interface-Based Edge Modes
The remarkable Cooper-like pairing phenomenon in the Aharonov-Bohm
interference of a Fabry-Perot interferometer (FPI)operating in the
integer quantum Hall regimeremains baffling. Here, we report the
interference of paired electrons employing 'interface edge modes'. These modes
are born at the interface between the bulk of the FPI and an outer gated region
tuned to a lower filling factor. Such configuration allows toggling the spin
and the orbital of the Landau level (LL) of the edge modes at the interface. We
find that electron pairing occurs only when the two modes (the interfering
outer and the first inner) belong to the same spinless LL.Comment: 21 pages, 10 figures, 1 table, Supplementary Informatio