13,830 research outputs found
Gas stripping in galaxy groups - the case of the starburst spiral NGC 2276
Ram pressure stripping of galactic gas is generally assumed to be inefficient
in galaxy groups due to the relatively low density of the intragroup medium and
the small velocity dispersions of groups. To test this assumption, we obtained
Chandra X-ray data of the starbursting spiral NGC 2276 in the NGC 2300 group of
galaxies, a candidate for a strong galaxy interaction with hot intragroup gas.
The data reveal a shock-like feature along the western edge of the galaxy and a
low-surface-brightness tail extending to the east, similar to the morphology
seen in other wavebands. Spatially resolved spectroscopy shows that the data
are consistent with intragroup gas being pressurized at the leading western
edge of NGC 2276 due to the galaxy moving supersonically through the intragroup
medium at a velocity ~850 km/s. Detailed modelling of the gravitational
potential of NGC 2276 shows that the resulting ram-pressure could significantly
affect the morphology of the outer gas disc but is probably insufficient to
strip large amounts of cold gas from the disc. We estimate the mass loss rates
due to turbulent viscous stripping and starburst outflows being swept back by
ram pressure, showing that both mechanisms could plausibly explain the presence
of the X-ray tail. Comparison to existing HI measurements shows that most of
the gas escaping the galaxy is in a hot phase. With a total mass loss rate of
roughly 5 M_Sun/yr, the galaxy could be losing its entire present HI supply
within a Gyr. This demonstrates that the removal of galactic gas through
interactions with a hot intragroup medium can occur rapidly enough to transform
the morphology of galaxies in groups. Implications of this for galaxy evolution
in groups and clusters are briefly discussed.Comment: 16 pages, 8 figures, accepted for publication in MNRA
Realizing time crystals in discrete quantum few-body systems
The exotic phenomenon of time translation symmetry breaking under periodic
driving - the time crystal - has been shown to occur in many-body systems even
in clean setups where disorder is absent. In this work, we propose the
realization of time-crystals in few-body systems, both in the context of
trapped cold atoms with strong interactions and of a circuit of superconducting
qubits. We show how these two models can be treated in a fairly similar way by
adopting an effective spin chain description, to which we apply a simple
driving protocol. We focus on the response of the magnetization in the presence
of imperfect pulses and interactions, and show how the results can be
interpreted, in the cold atomic case, in the context of experiments with
trapped bosons and fermions. Furthermore, we provide a set of realistic
parameters for the implementation of the superconducting circuit.Comment: 6 pages, 4 figure
Coupling of shells in a carbon nanotube quantum dot
We systematically study the coupling of longitudinal modes (shells) in a
carbon nanotube quantum dot. Inelastic cotunneling spectroscopy is used to
probe the excitation spectrum in parallel, perpendicular and rotating magnetic
fields. The data is compared to a theoretical model including coupling between
shells, induced by atomically sharp disorder in the nanotube. The calculated
excitation spectra show good correspondence with experimental data.Comment: 8 pages, 4 figure
Multiqubit State Learning with Entangling Quantum Generative Adversarial Networks
The increasing success of classical generative adversarial networks (GANs)
has inspired several quantum versions of GANs. Fully quantum mechanical
applications of such quantum GANs have been limited to one- and two-qubit
systems. In this paper, we investigate the entangling quantum GAN (EQ-GAN) for
multiqubit learning. We show that the EQ-GAN can learn a circuit more
efficiently compared to a swap test. We also consider the EQ-GAN for learning
VQE-approximated eigenstates, and find that it generates excellent overlap
matrix elements when learning VQE states of small molecules. However, this does
not directly translate to a good estimate of the energy due to a lack of phase
estimation. Finally, we consider random state learning with the EQ-GAN for up
to six qubits, using different two-qubit gates, and show that it is capable of
learning completely random quantum states, something which could be useful in
quantum state loading.Comment: 6 pages, 4 figures, 1 table + Supporting materia
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