We study the reduced time-evolution of open quantum systems by combining
quantum-information and statistical field theory. Inspired by prior work [EPL
102, 60001 (2013) and Phys. Rev. Lett. 111, 050402 (2013)] we establish the
explicit structure guaranteeing the complete positivity (CP) and
trace-preservation (TP) of the real-time evolution expansion in terms of the
microscopic system-environment coupling.

We present a system of equations and an explicit solution for the problem of
determining the MaxEnt state of a quantum system satisfying symmetry

Starting from a geometric perspective, we derive a quantum speed limit for
arbitrary open quantum evolution, which could be Markovian or non-Markovian,
providing a fundamental bound on the time taken for the most general quantum
dynamics. Our methods rely on measuring angles and distances between (mixed)
states represented as generalized Bloch vectors. We study the properties of our
bound and present its form for closed and open evolution, with the latter in

The No Low-Energy Trivial States (NLTS) conjecture of Freedman and Hastings
(Quantum Information and Computation 2014), which asserts the existence of
local Hamiltonians whose low energy states cannot be generated by constant
depth quantum circuits, identifies a fundamental obstacle to resolving the
quantum PCP conjecture. Progress towards the NLTS conjecture was made by Eldar
and Harrow (Foundations of Computer Science 2017), who proved a closely related

The multichannel Na-Cs interactions are characterized by a series of
measurements using two atoms in an optical tweezer, along with a multichannel
quantum defect theory (MQDT). The triplet and singlet scattering lengths are
measured by performing Raman spectroscopy of the Na-Cs motional states and
least-bound molecular state in the tweezer. Magnetic Feshbach resonances are
observed for only two atoms at fields which agree well with the MQDT. Our
methodology, which promotes the idea of an effective theory of interaction, can

We report, in a sequence of notes, our work on the Alibaba Cloud Quantum
Development Kit (AC-QDK). AC-QDK provides a set of tools for aiding the
development of both quantum computing algorithms and quantum processors, and is
powered by a large-scale classical simulator deployed on Alibaba Cloud. In this
note, we report the computational experiments demonstrating the classical
simulation capability of AC-QDK. We use as a benchmark the random quantum
circuits designed for Google's Bristlecone QPU {\cite{GRCS}}. We simulate

We investigate theoretically the dynamics of two quasi-degenerate orthogonal
mechanical modes of a suspended nanowire coupled to the two-level system of a
single-fluorescent molecule by Stark effect. We show that by driving the
molecular two-level system with a laser field one can engineer the effective
mechanical spectrum leading to an exceptional degeneracy point where the two
mechanical modes coalesce. It allows the topological actuation of the modes by

Quantum error correction protocols will play a central role in the
realisation of quantum computing; the choice of error correction code will
influence the full quantum computing stack, from the layout of qubits at the
physical level to gate compilation strategies at the software level. As such,
familiarity with quantum coding is an essential prerequisite for the
understanding of current and future quantum computing architectures. In this
review, we provide an introductory guide to the theory and implementation of

We propose a protocol for sympathetically cooling neutral atoms without
destroying the quantum information stored in their internal states. This is
achieved by designing state-insensitive Rydberg interactions between the
data-carrying atoms and cold auxiliary atoms. This can be used to extend the
lifetime of quantum storage based on neutral atoms and can have applications
for long quantum computations. The protocol can also be modified to realize
state-insensitive interactions between the data and the auxiliary atoms but

The increasing complexity of engineered quantum systems and devices raises
the need for efficient methods to verify that these systems are indeed
performing the desired quantum dynamics. Due to the inevitable coupling to
external environments, these methods should obtain not only the unitary part of
the dynamics, but also the dissipation and decoherence affecting the system's
dynamics. Here, we propose a method for reconstructing the Lindbladian
governing the Markovian dynamics of open many-body quantum systems, using data