# All

## Building quantum neural networks based on swap test. (arXiv:1904.12697v2 [quant-ph] UPDATED)

Artificial neural network, consisting of many neurons in different layers, is
an important method to simulate humain brain. Usually, one neuron has two
operations: one is linear, the other is nonlinear. The linear operation is
inner product and the nonlinear operation is represented by an activation
function. In this work, we introduce a kind of quantum neuron whose inputs and
outputs are quantum states. The inner product and activation operator of the
quantum neurons can be realized by quantum circuits. Based on the quantum

## A strengthened data processing inequality for the Belavkin-Staszewski relative entropy. (arXiv:1904.10768v2 [math-ph] CROSS LISTED)

In this work, we provide a strengthening of the data processing inequality
for the relative entropy introduced by Belavkin and Staszewski (BS-entropy).
This extends previous results by Carlen and Vershynina for the relative entropy
and other standard $f$-divergences. To this end, we provide two new equivalent
conditions for the equality case of the data processing inequality for the
BS-entropy. Subsequently, we extend our result to a larger class of maximal

## Many-Body Localization in the Presence of a Central Qudit

Author(s): Nathan Ng and Michael Kolodrubetz
We consider a many-body localized system coupled globally to a central $d$-level system. Under an appropriate scaling of $d$ and $L$, we find evidence that the localized phase survives. We argue for two possible thermalizing phases, depending on whether the qudit becomes fully ergodic. This system p...
[Phys. Rev. Lett. 122, 240402] Published Wed Jun 19, 2019

## Anonymity for Practical Quantum Networks

Author(s): Anupama Unnikrishnan, Ian J. MacFarlane, Richard Yi, Eleni Diamanti, Damian Markham, and Iordanis Kerenidis
Quantum communication networks have the potential to revolutionize information and communication technologies. Here we are interested in a fundamental property and formidable challenge for any communication network, that of guaranteeing the anonymity of a sender and a receiver when a message is tran...
[Phys. Rev. Lett. 122, 240501] Published Wed Jun 19, 2019

## Efficiency of a Quantum Otto Heat Engine Operating under a Reservoir at Effective Negative Temperatures

Author(s): Rogério J. de Assis, Taysa M. de Mendonça, Celso J. Villas-Boas, Alexandre M. de Souza, Roberto S. Sarthour, Ivan S. Oliveira, and Norton G. de Almeida
We perform an experiment in which a quantum heat engine works under two reservoirs, one at a positive spin temperature and the other at an effective negative spin temperature, i.e., when the spin system presents population inversion. We show that the efficiency of this engine can be greater than tha...
[Phys. Rev. Lett. 122, 240602] Published Wed Jun 19, 2019

## Energetic cost of quantum control protocols. (arXiv:1906.07201v1 [quant-ph])

We quantitatively assess the energetic cost of several well-known control
protocols that achieve a finite time adiabatic dynamics, namely counterdiabatic
and local counterdiabatic driving, optimal control, and inverse engineering. By
employing a cost measure based on the norm of the total driving Hamiltonian, we
show that a hierarchy of costs emerges that is dependent on the protocol
duration. As case studies we explore the Landau-Zener model, the quantum
harmonic oscillator, and the Jaynes-Cummings model and establish that

## Polarization-Based Truncated SU(1,1) Interferometer based on Four-wave Mixing in Rb vapor. (arXiv:1906.07213v1 [physics.optics])

We propose and demonstrate a polarization-based truncated SU(1,1)
interferometer that outputs the desired optical joint-quadrature of a two-mode
squeezed vacuum field and allows its measurements using a single balanced
homodyne detector. Using such setup we demonstrated up to $\approx$2 dB of
quantum noise suppression below the shot-noise limit in intensity-difference
and phase-sum joint quadratures, and confirmed entanglement between the two
quantum fields. Our proposed technique results in a better balance between the

## Evolution of quantum observables: from non-commutativity to commutativity. (arXiv:1906.07226v1 [quant-ph])

A fundamental aspect of the quantum-to-classical limit is the transition from
a non-commutative algebra of observables to commutative one. However, this
transition is not possible if we only consider unitary evolutions. One way to
describe this transition is to consider the Gamow vectors, which introduce
exponential decays in the evolution. In this paper, we give two mathematical
models in which this transition happens in the infite time limit. In the first

## Classical Linear Harmonic Oscillators to Describe Thermodynamic Properties of Quantum Linear Harmonic Oscillators and Solids. (arXiv:1906.07229v1 [cond-mat.stat-mech])

As known all physical properties of solids are described well by the system
of quantum linear harmonic oscillators. It is shown in the present paper that
the system consisting of classical linear harmonic oscillators having
temperature dependent masses or (and) frequencies has the same partition
function as the system consisting of quantum linear harmonic oscillators having
temperature independent masses and frequencies while the means of the square
displacements of the positions of the oscillators from their mean positions for

## Rank-deficient representations in Howe duality over finite fields arise from quantum codes. (arXiv:1906.07230v1 [math.RT])

Let V be a symplectic vector space and let $\mu$ be the oscillator
representation of Sp(V). It is natural to ask how the tensor power
representation $\mu^{\otimes t}$ decomposes. If V is a real vector space, then
Howe duality asserts that there is a one-one correspondence between the
irreducible subrepresentations of Sp(V) and the irreps of an orthogonal group
O(t). It is well-known that this duality fails over finite fields. Addressing
this situation, Gurevich and Howe have recently assigned a notion of rank to