Three new graph invariants are introduced which may be measured from a
quantum graph state and form examples of a framework under which other graph
invariants can be constructed. Each invariant is based on distinguishing a
different number of qubits. This is done by applying alternate measurements to
the qubits to be distinguished. The performance of these invariants is
evaluated and compared to classical invariants. We verify that the invariants
can distinguish all non-isomorphic graphs with 9 or fewer nodes. The invariants

Hybrid excitations, called polaritons, emerge in systems with strong
light-matter coupling. Usually, they dominate the linear and nonlinear optical
properties with applications in quantum optics. Here, we show the crucial role
of the electronic component of polaritons in the magneto-transport of a
cavity-embedded 2D electron gas in the ultrastrong coupling regime. We show
that the linear dc resistivity is significantly modified by the coupling to the
cavity even without external irradiation. Our observations confirm recent

The frustrated anisotropic four-leg spin-1/2 nanotube has been studied using
the real space quantum renormalization group (QRG) approach in the
thermodynamic limit. We have obtained the phase diagram, fixed points, critical
points, the scaling of coupling constants and magnetization curves. We have
shown that, in the case of strong leg coupling the diagonal frustrating
interaction is marginal under QRG transformations and does not affect the
universality class of the model. Remarkably, the renormalization equations

We present a method to derive experimentally accessible lower bounds for
measures of genuine multipartite entanglement (GME) and coherence. The method
works for several entanglement measures including the convex-roof extended
negativity, the concurrence of GME, the G-concurrence of GME, and the geometric
measure of GME. Moreover, the method also delivers observable lower bounds for
the convex roof of the $l_{1}$-norm of coherence, the geometric measure of

We study selective upconversion of optical signals according to their
detailed transverse electromagnetic modes, and demonstrate its proof of
operations in a nonlinear crystal. The mode selectivity is achieved by
preparing the pump wave in an optimized spatial profile to drive the
upconversion. For signals in the Laguerre-Gaussian modes, we show that a mode
can be converted with up to 60 times higher efficiency than an overlapping but
orthogonal mode. This nonlinear-optical approach may find applications in

As shown in Phys. Rev. A 96, 020101(R) (2017), it is possible to demonstrate
that quantum particles do not move along straight lines in free space by
increasing the probability of finding the particles within narrow intervals of
position and momentum beyond the "either/or" limit of 0.5 using constructive
quantum interference between a component localized in position and a component
localized in momentum. The probability of finding the particle in a
corresponding spatial interval at a later time then violates the lower bound of

We consider possible detection of nonclassicality of primordial gravitational
waves (PGWs) by applying Hanbury Brown - Twiss (HBT) interferometry to
cosmology. We characterize the nonclassicality of PGWs in terms of
sub-Poissonian statistics that can be measured by the HBT interferometry. We
show that the presence of classical sources during inflation makes us possible
to detect nonclassical PGWs with the HBT interferometry. We present two
examples that realize the classical sources during inflation. It turns out that

When a Bose-Einstein condensate rotates in a purely harmonic potential with
an angular frequency which is close to the trap frequency, its many-body state
becomes highly correlated, with the most well-known being the bosonic Laughlin
state. To take into account that in a real experiment no trapping potential is
ever exactly harmonic, we introduce an additional weak, quartic potential and
demonstrate that the Laughlin state is highly sensitive to this extra

Generating entanglement in a distributed scenario is a fundamental task for
implementing the quantum network of the future. We here report a protocol that
uses only linear optics for generating GHZ states with high fidelities in a
nearby node configuration. Moreover, we analytically show that the scheme
provides the highest success probability, and, then, the highest generation
rate for sequential protocols. We furthermore show how to retrieve the same

The generalized hyper-Ramsey resonance formula originally published in Phys.
Rev. A vol 92, 023416 (2015) is derived using a Cayley-Klein spinor
parametrization. The shape of the interferometric resonance and the associated
composite phase-shift are reformulated including all individual laser pulse
parameters. Potential robustness of signal contrast and phase-shift of the
wave-function fringe pattern can now be arbitrarily explored tracking any shape
distortion due to systematic effects from the probe laser. An exact and simple