45 research outputs found
Optimized protocols for duplex quantum transduction
Quantum transducers convert quantum signals through hybrid interfaces of
physical platforms in quantum networks. Modeled as quantum communication
channels, performance of unidirectional quantum transduction can be measured by
the quantum channel capacity. However, characterizing performance of quantum
transducers used for duplex quantum transduction where signals are converted
bidirectionally remains an open question. Here, we propose rate regions to
characterize the performance of duplex quantum transduction. Using this tool,
we find that quantum transducers optimized for simultaneous duplex transduction
can outperform strategies based on the standard protocol of time-shared
unidirectional transduction. Integrated over the frequency domain, we
demonstrate that rate region can also characterize quantum transducers with
finite bandwidth
Analysis of arbitrary superconducting quantum circuits accompanied by a Python package: SQcircuit
Superconducting quantum circuits are a promising hardware platform for
realizing a fault-tolerant quantum computer. Accelerating progress in this
field of research demands general approaches and computational tools to analyze
and design more complex superconducting circuits. We develop a framework to
systematically construct a superconducting quantum circuit's quantized
Hamiltonian from its physical description. As is often the case with quantum
descriptions of multicoordinate systems, the complexity rises rapidly with the
number of variables. Therefore, we introduce a set of coordinate
transformations with which we can find bases to diagonalize the Hamiltonian
efficiently. Furthermore, we broaden our framework's scope to calculate the
circuit's key properties required for optimizing and discovering novel qubits.
We implement the methods described in this work in an open-source Python
package SQcircuit. In this manuscript, we introduce the reader to the SQcircuit
environment and functionality. We show through a series of examples how to
analyze a number of interesting quantum circuits and obtain features such as
the spectrum, coherence times, transition matrix elements, coupling operators,
and the phase coordinate representation of eigenfunctions.Comment: 23 pages, 6 figures. Accompanying SQcircuit package on
https://sqcircuit.org
Measurement and correlation of liquid - Liquid equilibria of three imidazolium ionic liquids with acetone and cyclohexane
Ionic liquids (ILs) can be recycled as extractants for their low vapor pressure and volatility. More and more applications are applied to the separation of industrial organic matter. The industrial production of ILs has gradually been realized, which also widens the way for the application of ILs. In this work, the liquid-liquid extraction of cyclohexane-acetone azeotropic mixture with different ILs {1-butyl-3-methylimidazolium bis(trifluormethylsulfonyl), 1-butyl-3-methylimidazolium trifluoromethansulfonate and 1-butyl-3-methylimidazolium dicyanamide} is studied. The extraction mechanism is discussed based on the molecular scale. The relationship between hydrogen bond donor and acceptor between ILs and acetone is analyzed by COSMO-SAC. The interaction between molecules is optimized and calculated by Materials Studio 7.0. The extraction ability of ILs is analyzed by radial distribution function, and the experimental results are verified. The liquid-liquid equilibrium test is carried out at 298.15 K. Distribution and selectivity are indices used to judge the extraction efficiency of ILs. The NRTL model and UNIQUAC model are adopted to correlate the liquid-liquid equilibrium data. The results show that all of the two models can well correlate the experimental.This work is supported by the National Natural Science Foundation of China (No. 21776145), National Natural Science Foundation of China (No. 21676152)
Quantum state preparation, tomography, and entanglement of mechanical oscillators
Precisely engineered mechanical oscillators keep time, filter signals, and
sense motion, making them an indispensable part of today's technological
landscape. These unique capabilities motivate bringing mechanical devices into
the quantum domain by interfacing them with engineered quantum circuits.
Proposals to combine microwave-frequency mechanical resonators with
superconducting devices suggest the possibility of powerful quantum acoustic
processors. Meanwhile, experiments in several mechanical systems have
demonstrated quantum state control and readout, phonon number resolution, and
phonon-mediated qubit-qubit interactions. Currently, these acoustic platforms
lack processors capable of controlling multiple mechanical oscillators' quantum
states with a single qubit, and the rapid quantum non-demolition measurements
of mechanical states needed for error correction. Here we use a superconducting
qubit to control and read out the quantum state of a pair of nanomechanical
resonators. Our device is capable of fast qubit-mechanics swap operations,
which we use to deterministically manipulate the mechanical states. By placing
the qubit into the strong dispersive regime with both mechanical resonators
simultaneously, we determine the resonators' phonon number distributions via
Ramsey measurements. Finally, we present quantum tomography of the prepared
nonclassical and entangled mechanical states. Our result represents a concrete
step toward feedback-based operation of a quantum acoustic processor.Comment: 13 pages, 4+5 figure
Quantum dynamics of a few-photon parametric oscillator
Modulating the frequency of a harmonic oscillator at nearly twice its natural
frequency leads to amplification and self-oscillation. Above the oscillation
threshold, the field settles into a coherent oscillating state with a
well-defined phase of either or . We demonstrate a quantum parametric
oscillator operating at microwave frequencies and drive it into oscillating
states containing only a few photons. The small number of photons present in
the system and the coherent nature of the nonlinearity prevents the environment
from learning the randomly chosen phase of the oscillator. This allows the
system to oscillate briefly in a quantum superposition of both phases at once -
effectively generating a nonclassical Schr\"{o}dinger's cat state. We
characterize the dynamics and states of the system by analyzing the output
field emitted by the oscillator and implementing quantum state tomography
suited for nonlinear resonators. By demonstrating a quantum parametric
oscillator and the requisite techniques for characterizing its quantum state,
we set the groundwork for new schemes of quantum and classical information
processing and extend the reach of these ubiquitous devices deep into the
quantum regime