98 research outputs found
Accelerated quantum adiabatic transfer in superconducting qubits
Quantum adiabatic transfer is widely used in quantum computation and quantum
simulation. However, the transfer speed is limited by the quantum adiabatic
approximation condition, which hinders its application in quantum systems with
a short decoherence time. Here we demonstrate quantum adiabatic state transfers
that jump along geodesics in one-qubit and two-qubit superconducting transmons.
This approach possesses the advantages of speed, robustness, and high fidelity
compared with the usual adiabatic process. Our protocol provides feasible
strategies for improving state manipulation and gate operation in
superconducting quantum circuits
Analyzing Hidden Representations in End-to-End Automatic Speech Recognition Systems
Neural models have become ubiquitous in automatic speech recognition systems.
While neural networks are typically used as acoustic models in more complex
systems, recent studies have explored end-to-end speech recognition systems
based on neural networks, which can be trained to directly predict text from
input acoustic features. Although such systems are conceptually elegant and
simpler than traditional systems, it is less obvious how to interpret the
trained models. In this work, we analyze the speech representations learned by
a deep end-to-end model that is based on convolutional and recurrent layers,
and trained with a connectionist temporal classification (CTC) loss. We use a
pre-trained model to generate frame-level features which are given to a
classifier that is trained on frame classification into phones. We evaluate
representations from different layers of the deep model and compare their
quality for predicting phone labels. Our experiments shed light on important
aspects of the end-to-end model such as layer depth, model complexity, and
other design choices.Comment: NIPS 201
Simulating the Kibble-Zurek mechanism of the Ising model with a superconducting qubit system
The Kibble-Zurek mechanism (KZM) predicts the density of topological defects
produced in the dynamical processes of phase transitions in systems ranging
from cosmology to condensed matter and quantum materials. The similarity
between KZM and the Landau-Zener transition (LZT), which is a standard tool to
describe the dynamics of some non-equilibrium physics in contemporary physics,
is being extensively exploited. Here we demonstrate the equivalence between KZM
in the Ising model and LZT in a superconducting qubit system. We develop a
time-resolved approach to study quantum dynamics of LZT with nano-second
resolution. By using this technique, we simulate the key features of KZM in the
Ising model with LZT, e.g., the boundary between the adiabatic and impulse
regions, the freeze-out phenomenon in the impulse region, especially, the
scaling law of the excited state population as the square root of the quenching
rate. Our results supply the experimental evidence of the close connection
between KZM and LZT, two textbook paradigms to study the dynamics of the
non-equilibrium phenomena.Comment: Title changed, authors added, and some experimental data update
Sustainable and scalable in-situ synthesis of hydrochar-wrapped Ti3AlC2-derived nanofibers as adsorbents to remove heavy metals
To ensure a sustainable future, it is imperative to efficiently utilize abundant biomass to produce such as platform chemicals, transport fuels, and other raw materials; hydrochar is one of the promising candidates derived by hydrothermal carbonization of biomass in pressurized hot water. The synthesis of “hydrochar-wrapped Ti3AlC2-derived nanofibers” was successfully achieved by a facile one-pot hydrothermal reaction using glucose as the hydrochar precursor. Meanwhile, cellulose and pinewood sawdust as raw materials were also investigated. Products were characterized by XRD, N2 adsorption-desorption isotherms, SEM, TEM and FT-IR to investigate their crystal structures, textural properties, morphologies, and surface species. In the adsorption test to remove Cd(II) and Cu(II) in aqueous solution, hydrochar-wrapped nanofibers outperformed pure nanofibers derived from Ti3AlC2, hydrothermal carbon derived from glucose and commercial activated carbon. Finally, the regeneration, sorption kinetics, and possible adsorption mechanism were also explored
Experimental Implementation of Noncyclic and Nonadiabatic Geometric Quantum Gates in a Superconducting Circuit
Quantum gates based on geometric phases possess intrinsic noise-resilience
features and therefore attract much attention. However, the implementations of
previous geometric quantum computation typically require a long pulse time of
gates. As a result, their experimental control inevitably suffers from the
cumulative disturbances of systematic errors due to excessive time consumption.
Here, we experimentally implement a set of noncyclic and nonadiabatic geometric
quantum gates in a superconducting circuit, which greatly shortens the gate
time. And also, we experimentally verify that our universal single-qubit
geometric gates are more robust to both the Rabi frequency error and qubit
frequency shift-induced error, compared to the conventional dynamical gates, by
using the randomized benchmarking method. Moreover, this scheme can be utilized
to construct two-qubit geometric operations, while the generation of the
maximally entangled Bell states is demonstrated. Therefore, our results provide
a promising routine to achieve fast, high-fidelity, and error-resilient quantum
gates in superconducting quantum circuits
- …