We analyze the dynamics of multiparticle discrete-time quantum walk on the
two-dimensional lattice, with an interaction inspired on a classical model for
gas collision, called HPP model. In this classical model, the direction of
motion changes only when the particles collide head-on, preserving momentum and
energy. In our quantum model, the dynamics is driven by the usual quantum-walk
evolution operator if the particles are on different nodes, and is driven by

Floquet engineering or coherent time periodic driving of quantum systems has
been successfully used to synthesize Hamiltonians with novel properties. In
ultracold atomic systems, this has led to experimental realizations of
artificial gauge fields, topological band structures, and observation of
dynamical localization, to name just a few. Here we present a Floquet-based
framework to stroboscopically engineer Hamiltonians with spatial features and
periodicity below the diffraction limit of light used to create them by

History dependent discrete time quantum walks (QWs) are often studied for
their lattice traversal properties. A particular model in the literature uses
the state of a memory qubit at each site to record visits and to control the
dynamics of the walk. We generalize this model to the neighborhood-history
quantum walk (NHQW), in which the walk dynamics and the state of the memory
qubits in a neighborhood of the particle's position are interdependent. To
demonstrate it, we construct an NHQW on a one-dimensional lattice, with a

Quantum annealing is a heuristic algorithm for solving combinatorial
optimization problems, and D-Wave Systems Inc. has developed hardware for
implementing this algorithm. The current version of the D-Wave quantum annealer
can solve unconstrained binary optimization problems with a limited number of
binary variables, although cost functions of many practical problems are
defined by a large number of integer variables. To solve these problems with
the quantum annealer, the integer variables are generally binarized with

We propose and discuss a method to engineer stroboscopically arbitrary
one-dimensional optical potentials with subwavelength resolution. Our approach
is based on subwavelength optical potential barriers for atoms in the dark
state in an optical \Lambda system, which we use as a stroboscopic drawing tool
by controlling their amplitude and position by changing the amplitude and the
phase of the control Rabi frequency in the \Lambda system. We demonstrate the

We theoretically analyze the performance of the nuclear magnetic resonance
(NMR) spectroscopy with a superconducting flux qubit (FQ). Such NMR with the FQ
is attractive because of the possibility to detect the relatively small number
of nuclear spins in a local region ($\sim\mu$m) with low temperatures ($\sim$
mK) and low magnetic fields ($\sim$ mT), in which other types of quantum
sensing schemes cannot easily access. A sample containing nuclear spins is

Squeezed states of light have received renewed attention due to their
applicability to quantum-enhanced sensing. To take full advantage of their
reduced noise properties to enhance atomic-based sensors, it is necessary to
generate narrowband near or on atomic resonance single-mode squeezed states of
light. We have previously generated bright two-mode squeezed states of light,
or twin beams, that can be tuned to resonance with the D1 line of $^{87}$Rb
with a non-degenerate four-wave mixing (FWM) process in a double-lambda

We present a novel continuous-time control strategy to exponentially
stabilize an eigenstate of a Quantum Non-Demolition (QND) measurement operator.
In open-loop, the system converges to a random eigenstate of the measurement
operator. The role of the feedback is to prepare a prescribed QND eigenstate
with unit probability. To achieve this we introduce the use of Brownian motion
to drive the unitary control actions; the feedback loop just adapts the
amplitude of this Brownian noise input as a function of the system state.

We looked into the algorithm for calculating Betti numbers presented by
Lloyd, Garnerone, and Zanardi (LGZ). We present a new algorithm in the same
spirit as LGZ with the intent of clarifying quantum algorithms for computing
Betti numbers. Our algorithm is simpler and slightly more efficient than that
presented by LGZ. We present a thorough analysis of our algorithm, pointing out
reasons that both our algorithm and that presented by LGZ do not run in
polynomial time for most inputs. However, the algorithms do run in polynomial

We derive the full linear-response theory for non-relativistic quantum
electrodynamics in the long wavelength limit, show quantum modifications of the
well-known Maxwell's equation in matter and provide a practical framework to
solve the resulting equations by using quantum-electrodynamical
density-functional theory. We highlight how the coupling between quantized
light and matter changes the usual response functions and introduces new types
of cross-correlated light-matter response functions. These cross-correlation