A method to study strongly interacting quantum many-body systems at and away
from criticality is proposed. The method is based on a MERA-like tensor network
that can be efficiently and reliably contracted on a noisy quantum computer
using a number of qubits that is much smaller than the system size. We prove
that the outcome of the contraction is stable to noise and that the estimated
energy upper bounds the ground state energy. The stability, which we
numerically substantiate, follows from the positivity of operator scaling

The coupling between defects in diamond and a superconducting microwave
resonator is studied in the nonlinear regime. Both negatively charged
nitrogen-vacancy and P1 defects are explored. The measured cavity mode response
exhibits strong nonlinearity near a spin resonance. Data is compared with
theoretical predictions and a good agreement is obtained. The nonlinear effect
under study in the current paper is expected to play a role in any cavity-based
magnetic resonance imaging technique and to impose a fundamental limit upon its

Phase collapse and revival for Bose-Einstein condensates is a nonlinear
phenomena appearing due atomic collisions. While it has been observed in a
general setting involving many modes, for one-mode condensates its occurrence
is forbidden by the particle number superselection rule (SSR), which arises
because there is no phase reference available. We consider a single mode atomic
Bose-Einstein condensate interacting with an off-resonant optical probe field.

Atomic systems display a rich variety of quantum dynamics due to the
different possible symmetries obeyed by the atoms. These symmetries result in
selection rules that have been essential for the quantum control of atomic
systems. Superconducting artificial atoms are mainly governed by parity
symmetry. Its corresponding selection rule limits the types of quantum systems
that can be built using electromagnetic circuits at their optimal coherence
operation points ("sweet spots"). Here, we use third-order nonlinear coupling

We study the dynamics of microscopic quantum correlations, viz., bipartite
entanglement and quantum discord, in Ising spin chain with periodically varying
external magnetic field along the transverse direction. Depending upon system
parameters, the local quantum correlations in the evolved states of such
systems may get saturated to non-zero values after sufficiently large number of
driving cycles. Moreover, we investigate convergence of the local density

We present design and simulation of a Josephson parametric amplifier with
bandwidth exceeding 1.6 GHz, and with high saturation power approaching -90 dBm
at a gain of 22.8 dB. An improvement by a factor of roughly 50 in bandwidth
over the state of the art is achieved by using well-established impedance
matching techniques. An improvement by a factor of roughly 100 in saturation
power over the state of the art is achieved by implementing the Josephson
nonlinear element as an array of rf-SQUIDs with a total of 40 junctions.

We perform time-dependent analysis of quantum dynamics of dark matter
particles in the Solar System. It is shown that this problem has similarities
with a microwave ionization of Rydberg atoms studied previously experimentally
and analytically. On this basis it is shown that the quantum effects for
chaotic dark matter dynamics become significant for dark matter mass ratio to
electron mass being smaller than $2 \times 10^{-15}$. Below this border
multiphoton diffusion over Rydberg states of dark matter atom becomes

The search for new, application-specific quantum computers designed to
outperform any classical computer is driven by the ending of Moore's law and
the quantum advantages potentially obtainable. Photonic networks are promising
examples, with experimental demonstrations and potential for obtaining a
quantum computer to solve problems believed classically impossible. This
introduces a challenge: how does one design or understand such photonic
networks? We develop novel complex phase-space software for simulating these

One of the most remarkable properties of the nitrogen-vacancy (NV) center in
diamond is that optical illumination initializes its electronic spin almost
completely, a feature that can be exploited to polarize other spin species in
their proximity. Here we use field-cycled nuclear magnetic resonance (NMR) to
investigate the mechanisms of spin polarization transfer from NVs to 13C spins
in diamond at room temperature. We focus on the dynamics near 51 mT, where a

Clarifying the impact of quantumness in the operation and properties of
thermal machines represents a major challenge. Here we envisage a toy model
acting either as an information-driven fridge or as heat-powered information
eraser in which coherences can be naturally introduced in by means of squeezed
thermal reservoirs. We study the validity of the transient entropy production
fluctuation theorem in the model with and without squeezing as well as its
decomposition into adiabatic and non-adiabatic contributions. Squeezing