5,382 research outputs found
Bogoliubov theory of entanglement in a Bose-Einstein condensate
We consider a Bose-Einstein condensate which is illuminated by a short
resonant light pulse that coherently couples two internal states of the atoms.
We show that the subsequent time evolution prepares the atoms in an interesting
entangled state called a spin squeezed state. This evolution is analysed in
detail by developing a Bogoliubov theory which describes the entanglement of
the atoms. Our calculation is a consistent expansion in , where
is the number of particles in the condensate, and our theory predict that it is
possible to produce spin squeezing by at least a factor of . Within
the Bogoliubov approximation this result is independent of temperature.Comment: 14 pages, including 5 figures, minor changes in the presentatio
Approximate Well-supported Nash Equilibria below Two-thirds
In an epsilon-Nash equilibrium, a player can gain at most epsilon by changing
his behaviour. Recent work has addressed the question of how best to compute
epsilon-Nash equilibria, and for what values of epsilon a polynomial-time
algorithm exists. An epsilon-well-supported Nash equilibrium (epsilon-WSNE) has
the additional requirement that any strategy that is used with non-zero
probability by a player must have payoff at most epsilon less than the best
response. A recent algorithm of Kontogiannis and Spirakis shows how to compute
a 2/3-WSNE in polynomial time, for bimatrix games. Here we introduce a new
technique that leads to an improvement to the worst-case approximation
guarantee
The Ground State Energy of Heavy Atoms According to Brown and Ravenhall: Absence of Relativistic Effects in Leading Order
It is shown that the ground state energy of heavy atoms is, to leading order,
given by the non-relativistic Thomas-Fermi energy. The proof is based on the
relativistic Hamiltonian of Brown and Ravenhall which is derived from quantum
electrodynamics yielding energy levels correctly up to order Ry
Græsmarksafgrødernes sammensætning – en kompleks sag
Ønsker man at producere mælk med
en given sammensætning, er det vigtigt
både at fokusere på anvendelsen af forskellige
græssorter samt at have fokus på
planternes udviklingstrin
Doped coupled frustrated spin-1/2 chains with four-spin exchange
The role of various magnetic inter-chain couplings is investigated by
numerical methods in doped frustrated quantum spin chains. A non-magnetic
dopant introduced in a gapped spin chain releases a free spin-1/2 soliton. The
formation of a local magnetic moment is analyzed in term of soliton
confinement. A four-spin coupling which might originate from cyclic exchange is
shown to produce such a confinement in contrast to transverse magnetic
exchange. Dopants on different chains experience an effective space-extended
non-frustrating pairwise spin interaction.Comment: Few modifications and references added. Submitted to PR
Spin Squeezing in the Ising Model
We analyze the collective spin noise in interacting spin systems. General
expressions are derived for the short time behaviour of spin systems with
general spin-spin interactions, and we suggest optimum experimental conditions
for the detection of spin squeezing. For Ising models with site dependent
nearest neighbour interactions general expressions are presented for the spin
squeezing parameter for all times. The reduction of collective spin noise can
be used to verify the entangling powers of quantum computer architectures based
on interacting spins.Comment: 7 pages, including 3 figure
- …