We study quantum period finding algorithms such as Simon, Shor, and
Eker{\aa}-H{\aa}stad. For a periodic function $f$ these algorithms produce --
via some quantum embedding of $f$ -- a quantum superposition $\sum_x \vert
x\rangle\vert f(x)\rangle$, which requires a certain amount of output bits that
represent $\vert f(x)\rangle$. We show that we can lower this amount to a
single output qubit by hashing $f$ down to a single bit. Namely, we replace the
embedding of $f$ in quantum period finding circuits by several embeddings of

We study the dynamics of coupled quantum spins one-half on a lattice with
nearest-neighbour "XY" (flip-flop) interactions, driven by external fields and
subject to dissipation. The meanfield limit of the model manifests bistable
parameter regions of two coexisting steady states with different
magnetizations. We introduce an efficient scheme accounting for the corrections
to meanfield by correlations at leading order, and benchmark this scheme using
high-precision numerics based on matrix-product-operators in one- and

In 1935, in a paper entitled "Can quantum-mechanical description of reality
be considered complete?", Einstein, Podolsky, and Rosen (EPR) formulated an
apparent paradox of quantum theory. They considered two quantum systems that
were initially allowed to interact, and were then later separated. A
measurement of a physical observable performed on one system then had to have
an immediate effect on the conjugate observable in the other system - even if
the systems were causally disconnected! The authors viewed this as a clear

The scalar product of two vectors with $K$ real components can be computed
using two quantum channels, that is, information transmission lines in the form
of spin-1/2 XX chains. Each channel has its own $K$-qubit sender and both
channels share a single two-qubit receiver. The $K$ elements of each vector are
encoded in the pure single-excitation initial states of the senders. After time
evolution, a bi-linear combination of these elements appears in the only matrix

We study two recent conjectures for holographic complexity: the
complexity=action conjecture and the complexity=volume conjecture. In
particular, we examine the structure of the UV divergences appearing in these
quantities, and show that the coefficients can be written as local integrals of
geometric quantities in the boundary. We also consider extending these
conjectures to evaluate the complexity of the mixed state produced by reducing
the pure global state to a specific subregion of the boundary time slice. The

Probing optical excitations with nanometer resolution is important for
understanding their dynamics and interactions down to the atomic scale.
Electron microscopes currently offer the unparalleled ability of rendering
spatially-resolved electron spectra with combined meV and sub-nm resolution,
while the use of ultrafast optical pulses enables fs temporal resolution and
exposure of the electrons to ultraintense confined optical fields. Here, we
theoretically investigate fundamental aspects of the interaction of fast

In this paper, we report a numerical method for analyzing optical radiation
from a two-level atom. The proposed method can consistently consider the
optical emission and absorption process of an atom, and also the interaction
between atoms through their interaction with a radiation field. The numerical
model is based on a damping oscillator description of a dipole current, which
is a classical model of atomic transition and is implemented with a
finite-difference time-domain method. Using the method, we successfully

Summoning is a task between two parties, Alice and Bob, with distributed
networks of agents in space-time. Bob gives Alice a random quantum state, known
to him but not her, at some point. She is required to return the state at some
later point, belonging to a subset defined by communications received from Bob
at other points. Many results about summoning, including the impossibility of
unrestricted summoning tasks and the necessary conditions for specific types of

An experiment to test for relativistic frame dragging effects with quantum
interferometry is proposed. The idea that the classical trajectories of the
interferometer surround a spherical mass source whose angular momentum is
perpendicular to the plane containing these trajectories. A simple analysis
allows one to find the phase shift for particles traveling in the innermost
stable circular orbit; the result can be easily generalized for more realistic
orbits. The phase difference goes like the source's angular momentum per mass

Bright squeezed vacuum (BSV) is a non-classical macroscopic state of light,
which can be generated through high-gain parametric down-conversion or
four-wave mixing. Although BSV is an important tool in quantum optics and has a
lot of applications, its theoretical description is still not complete. In
particular, the existing description in terms of Schmidt modes fails to explain
the spectral broadening observed in experiment as the mean number of photons