3,137,076 research outputs found

### Ground State Electroluminescence

Electroluminescence, the emission of light in the presence of an electric
current, provides information on the allowed electronic transitions of a given
system. It is commonly used to investigate the physics of strongly-coupled
light-matter systems, whose eigenfrequencies are split by the strong coupling
with the photonic field of a cavity. Here we show that, together with the usual
electroluminescence, systems in the ultrastrong light-matter coupling regime
emit a uniquely quantum radiation when a flow of current is driven through
them. While standard electroluminescence relies on the population of excited
states followed by spontaneous emission, the process we describe herein
extracts bound photons by the dressed ground state and it has peculiar features
that unequivocally distinguish it from usual electroluminescence.Comment: 6 pages, 3 figure

### Multielectron Ground State Electroluminescence

The ground state of a cavity-electron system in the ultrastrong coupling
regime is characterized by the presence of virtual photons. If an electric
current flows through this system, the modulation of the light-matter coupling
induced by this non-equilibrium effect can induce an extra-cavity photon
emission signal, even when electrons entering the cavity do not have enough
energy to populate the excited states. We show that this ground-state
electroluminescence, previously identified in a single-qubit system [Phys. Rev.
Lett. 116, 113601 (2016)] can arise in a many-electron system. The collective
enhancement of the light-matter coupling makes this effect, described beyond
the rotating wave approximation, robust in the thermodynamic limit, allowing
its observation in a broad range of physical systems, from a semiconductor
heterostructure with flat-band dispersion to various implementations of the
Dicke model.Comment: 32 pages (9+23), 9 figures (3+6

### Ground State Quantum Computation

We formulate a novel ground state quantum computation approach that requires
no unitary evolution of qubits in time: the qubits are fixed in stationary
states of the Hamiltonian. This formulation supplies a completely
time-independent approach to realizing quantum computers. We give a concrete
suggestion for a ground state quantum computer involving linked quantum dots.Comment: 4 pages, 2 figure

### Ground State Entanglement Energetics

We consider the ground state of simple quantum systems coupled to an
environment. In general the system is entangled with its environment. As a
consequence, even at zero temperature, the energy of the system is not sharp: a
projective measurement can find the system in an excited state. We show that
energy fluctuation measurements at zero temperature provide entanglement
information. For two-state systems which exhibit a persistent current in the
ground state, energy fluctuations and persistent current fluctuations are
closely related. The harmonic oscillator serves to illustrate energy
fluctuations in a system with an infinite number of states. In addition to the
energy distribution we discuss the energy-energy time-correlation function in
the zero-temperature limit.Comment: 10 pages, 6 figure

### Ground State Spin Logic

Designing and optimizing cost functions and energy landscapes is a problem
encountered in many fields of science and engineering. These landscapes and
cost functions can be embedded and annealed in experimentally controllable spin
Hamiltonians. Using an approach based on group theory and symmetries, we
examine the embedding of Boolean logic gates into the ground state subspace of
such spin systems. We describe parameterized families of diagonal Hamiltonians
and symmetry operations which preserve the ground state subspace encoding the
truth tables of Boolean formulas. The ground state embeddings of adder circuits
are used to illustrate how gates are combined and simplified using symmetry.
Our work is relevant for experimental demonstrations of ground state embeddings
found in both classical optimization as well as adiabatic quantum optimization.Comment: 6 pages + 3 pages appendix, 7 figures, 1 tabl

### Magnetic Excitations in the Ground State of $\mathrm{Yb_2Ti_2O_7}$

We report an extensive study on the zero field ground state of a powder
sample of the pyrochlore $\mathrm{Yb_2Ti_2O_7}$. A sharp heat capacity anomaly
that labels a low temperature phase transition in this material is observed at
280 mK. Neutron diffraction shows that a \emph{quasi-collinear} ferromagnetic
order develops below $T_\mathrm{c}$ with a magnetic moment of
$0.87(2)\mu_\mathrm{B}$. High resolution inelastic neutron scattering
measurements show, below the phase transition temperature, sharp gapped
low-lying magnetic excitations coexisting with a remnant quasielastic
contribution likely associated with persistent spin fluctuations. Moreover, a
broad inelastic continuum of excitations at $\sim0.6$ meV is observed from the
lowest measured temperature up to at least 2.5 K. At 10 K, the continuum has
vanished and a broad quasielastic conventional paramagnetic scattering takes
place at the observed energy range. Finally, we show that the exchange
parameters obtained within the framework of linear spin-wave theory do not
accurately describe the observed zero field inelastic neutron scattering data.Comment: 11 pages, 9 figures, Phys. Rev. B. (accepted

### Atomic Ground-State Energies

It is demonstrated that atomic Hartree–Fock binding energies may be reproduced with great accuracy (within about four parts in a thousand) by a scaled model system in which the electrons are noninteracting, and are bound in a bare Coulomb potential. </jats:p

### Magnetic ground state of FeSe

Elucidating the nature of the magnetism of a high-temperature superconductor
is crucial for establishing its pairing mechanism. The parent compounds of the
cuprate and iron-pnictide superconductors exhibit N\'eel and stripe magnetic
order, respectively. However, FeSe, the structurally simplest iron-based
superconductor, shows nematic order (Ts = 90 K), but not magnetic order in the
parent phase, and its magnetic ground state is intensely debated. Here, we
report inelastic neutron-scattering experiments that reveal both stripe and
N\'eel spin fluctuations over a wide energy range at 110 K. On entering the
nematic phase, a substantial amount of spectral weight is transferred from the
N\'eel to the stripe spin fluctuations. Moreover, the total fluctuating
magnetic moment of FeSe is ~ 60% larger than that in the iron pnictide
BaFe2As2. Our results suggest that FeSe is a novel S = 1 nematic
quantum-disordered paramagnet interpolating between the N\'eel and stripe
magnetic instabilities.Comment: Supplementary information included; accepted by Nature Communication

### Spin of ground state baryons

We calculate the quark spin contribution to the total angular momentum of
flavor octet and flavor decuplet ground state baryons using a spin-flavor
symmetry based parametrization method of quantum chromodynamics. We find that
third order SU(6) symmetry breaking three-quark operators are necessary to
explain the experimental result Sigma_1=0.32(10). For spin 3/2 decuplet baryons
we predict that the quark spin contribution is Sigma_3=3.93(22), i.e.
considerably larger than their total angular momentum.Comment: 8 page

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