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Quantum Renyi relative entropies provide a one-parameter family of distances
between density matrices, which generalizes the relative entropy and the
fidelity. We study these measures for renormalization group flows in quantum
field theory. We derive explicit expressions in free field theory based on the
real time approach. Using monotonicity properties, we obtain new inequalities
that need to be satisfied by consistent renormalization group trajectories in
field theory. These inequalities play the role of a second law of

We use concurrence as an entanglement measure and experimentally demonstrate
the entanglement classification of arbitrary three-qubit pure states on a
nuclear magnetic resonance (NMR) quantum information processor. Computing the
concurrence experimentally under three different bipartitions, for an arbitrary
three-qubit pure state, reveals the entanglement class of the state. The
experiment involves measuring the expectation values of Pauli operators. This
was achieved by mapping the desired expectation values onto the local $z$

Quantum computers can offer dramatic improvements over classical devices for
data analysis tasks such as prediction and classification. However, less is
known about the advantages that quantum computers may bring in the setting of
reinforcement learning, where learning is achieved via interaction with a task
environment. Here, we consider a special case of reinforcement learning, where
the task environment allows quantum access. In addition, we impose certain

The correlations of certain entangled quantum states can be fully reproduced
via a local model. We discuss in detail the practical implementation of an
algorithm for constructing local models for entangled states, recently
introduced by Hirsch et al. [Phys. Rev. Lett. 117, 190402 (2016)] and
Cavalcanti et al. [Phys. Rev. Lett. 117, 190401 (2016)]. The method allows one
to construct both local hidden state (LHS) and local hidden variable (LHV)
models, and can be applied to arbitrary entangled states in principle. Here we

The recent years have seen a growing interest in quantum codes in three
dimensions (3D). One of the earliest proposed 3D quantum codes is the 3D toric
code. It has been shown that 3D color codes can be mapped to 3D toric codes.
The 3D toric code on cubic lattice is also a building block for the welded code
which has highest energy barrier to date. Although well known, the performance
of the 3D toric code has not been studied extensively. In this paper, we

In the quantum control process, arbitrary pure or mixed initial states need
to be protected from amplitude damping through the noise channel using
measurements and quantum control. However, how to achieve it on a two-qubit
quantum system remains a challenge. In this paper, we propose a feed-forward
control approach to protect arbitrary two-qubit pure or mixed initial states
using the weak measurement. A feed-forward operation and measurements are used
before the noise channel, and afterwards a reversed operation and measurements

The quantum simulation of quantum chemistry is a promising application of
quantum computers. However, for N molecular orbitals, the $\mathcal{O}(N^4)$
gate complexity of performing Hamiltonian and unitary Coupled Cluster Trotter
steps makes simulation based on such primitives challenging. We substantially
reduce the gate complexity of such primitives through a two-step low-rank
factorization of the Hamiltonian and cluster operator, accompanied by
truncation of small terms. Using truncations that incur errors below chemical

We consider circuit complexity in certain interacting scalar quantum field
theories, mainly focusing on the $\phi^4$ theory. We work out the circuit
complexity for evolving from a nearly Gaussian unentangled reference state to
the entangled ground state of the theory. Our approach uses Nielsen's geometric
method, which translates into working out the geodesic equation arising from a
certain cost functional. We present a general method, making use of integral

We study the eigenstates of quantum systems with large Hilbert spaces, via
their distribution of wavefunction amplitudes in a real-space basis. For
single-particle 'quantum billiards', these real-space amplitudes are known to
have Gaussian distribution for chaotic systems. In this work, we formulate and
address the corresponding question for many-body lattice quantum systems. For
integrable many-body systems, we examine the deviation from Gaussianity and
provide evidence that the distribution generically tends toward power-law

Using the Wigner approach, we propose an inequality to test the macroscopic
realism concept. The proposed inequality is first derived for three distinct
moments of time and then for $n$ distinct moments of time. Using the latter one
we show that any unitary evolution of a quantum system contradicts the concept
of macroscopic realism. We also obtain an inequality for testing of the
hypothesis of realism. It is shown that this inequality is not identical to the
Wigner inequality.