458 research outputs found
Realistic Area-Law Bound on Entanglement from Exponentially Decaying Correlations
A remarkable feature of typical ground states of strongly-correlated
many-body systems is that the entanglement entropy is not an extensive
quantity. In one dimension, there exists a proof that a finite correlation
length sets a constant upper-bound on the entanglement entropy, called the area
law. However, the known bound exists only in a hypothetical limit, rendering
its physical relevance highly questionable. In this paper, we give a simple
proof of the area law for entanglement entropy in one dimension under the
condition of exponentially decaying correlations. Our proof dramatically
reduces the previously known bound on the entanglement entropy, bringing it,
for the first time, into a realistic regime. The proof is composed of several
simple and straightforward steps based on elementary quantum information tools.
We discuss the underlying physical picture, based on a renormalization-like
construction underpinning the proof, which transforms the entanglement entropy
of a continuous region into a sum of mutual informations in different length
scales and the entanglement entropy at the boundary
Addressing individual atoms in optical lattices with standing-wave driving fields
A scheme for addressing individual atoms in one- or two-dimensional optical
lattices loaded with one atom per site is proposed. The scheme is based on
position-dependent atomic population transfer induced by several standing-wave
driving fields. This allows various operations important in quantum information
processing, such as manipulation and measurement of any single atom, two-qubit
operations between any pair of adjacent atoms, and patterned loading of the
lattice with one atom per every nth site for arbitrary n. The proposed scheme
is robust against considerable imperfections and actually within reach of
current technology.Comment: 4 pages, 3 figures; minor revision
Generation of Atomic Cluster States through the Cavity Input-Output Process
We propose a scheme to implement a two-qubit controlled-phase gate for single
atomic qubits, which works in principle with nearly ideal success probability
and fidelity. Our scheme is based on the cavity input-output process and the
single photon polarization measurement. We show that, even with the practical
imperfections such as atomic spontaneous emission, weak atom-cavity coupling,
violation of the Lamb-Dicke condition, cavity photon loss, and detection
inefficiency, the proposed gate is feasible for generation of a cluster state
in that it meets the scalability criterion and it operates in a conclusive
manner. We demonstrate a simple and efficient process to generate a cluster
state with our high probabilistic entangling gate
Two-dimensional imaging of gauge fields in optical lattices
We propose a scheme to generate an arbitrary Abelian vector potential for
atoms trapped in a two-dimensional optical lattice. By making the optical
lattice potential dependent on the atomic state, we transform the problem into
that of a two-dimensional imaging. It is shown that an arbitrarily fine pattern
of the gauge field in the lattice can be realized without need of
diffraction-limited imaging.Comment: 4 pages, 3 figure
An emergent geometric description for a topological phase transition in the Kitaev superconductor model
Resorting to Wilsonian renormalization group (RG) transformations, we propose
an emergent geometric description for a topological phase transition in the
Kitaev superconductor model. An effective field theory consists of an emergent
bulk action with an extra dimension, an ultraviolet (UV) boundary condition for
an initial value of a coupling function, and an infrared (IR) effective action
with a fully renormalized coupling function. The bulk action describes the
evolution of the coupling function along the direction of the extra dimension,
where the extra dimension is identified with an RG scale and the resulting
equation of motion is nothing but a function. In particular, the IR
effective field theory turns out to be consistent with a Callan-Symanzik
equation which takes into account both the bulk and IR boundary contributions.
This derived Callan-Symanzik equation gives rise to a metric structure. Based
on this emergent metric tensor, we uncover the equivalence of the entanglement
entropy between the emergent geometric description and the quantum field theory
in the vicinity of the quantum critical point.Comment: Two figures adde
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