38 research outputs found
Topological pumping of photons in nonlinear resonator arrays
We show how to implement topological or Thouless pumping of interacting
photons in one dimensional nonlinear resonator arrays, by simply modulating the
frequency of the resonators periodically in space and time. The interplay
between interactions and the adiabatic modulations enables robust transport of
Fock states with few photons per site. We analyze the transport mechanism via
an effective analytic model and study its topological properties and its
protection to noise. We conclude by a detailed study of an implementation with
existing circuit QED architectures.Comment: 5 pages, 4 figures, and Supplemental Material. Comments are welcom
Topological Surface States Protected From Backscattering by Chiral Spin Texture
Topological insulators are a new class of insulators in which a bulk gap for
electronic excitations is generated by strong spin orbit coupling. These novel
materials are distinguished from ordinary insulators by the presence of gapless
metallic boundary states, akin to the chiral edge modes in quantum Hall
systems, but with unconventional spin textures. Recently, experiments and
theoretical efforts have provided strong evidence for both two- and
three-dimensional topological insulators and their novel edge and surface
states in semiconductor quantum well structures and several Bi-based compounds.
A key characteristic of these spin-textured boundary states is their
insensitivity to spin-independent scattering, which protects them from
backscattering and localization. These chiral states are potentially useful for
spin-based electronics, in which long spin coherence is critical, and also for
quantum computing applications, where topological protection can enable
fault-tolerant information processing. Here we use a scanning tunneling
microscope (STM) to visualize the gapless surface states of the
three-dimensional topological insulator BiSb and to examine their scattering
behavior from disorder caused by random alloying in this compound. Combining
STM and angle-resolved photoemission spectroscopy, we show that despite strong
atomic scale disorder, backscattering between states of opposite momentum and
opposite spin is absent. Our observation of spin-selective scattering
demonstrates that the chiral nature of these states protects the spin of the
carriers; they therefore have the potential to be used for coherent spin
transport in spintronic devices.Comment: to be appear in Nature on August 9, 200
Optimizing quantum gates towards the scale of logical qubits
A foundational assumption of quantum error correction theory is that quantum
gates can be scaled to large processors without exceeding the error-threshold
for fault tolerance. Two major challenges that could become fundamental
roadblocks are manufacturing high performance quantum hardware and engineering
a control system that can reach its performance limits. The control challenge
of scaling quantum gates from small to large processors without degrading
performance often maps to non-convex, high-constraint, and time-dependent
control optimization over an exponentially expanding configuration space. Here
we report on a control optimization strategy that can scalably overcome the
complexity of such problems. We demonstrate it by choreographing the frequency
trajectories of 68 frequency-tunable superconducting qubits to execute single-
and two-qubit gates while mitigating computational errors. When combined with a
comprehensive model of physical errors across our processor, the strategy
suppresses physical error rates by compared with the case of no
optimization. Furthermore, it is projected to achieve a similar performance
advantage on a distance-23 surface code logical qubit with 1057 physical
qubits. Our control optimization strategy solves a generic scaling challenge in
a way that can be adapted to other quantum algorithms, operations, and
computing architectures