arXiv subjects

Anders Sorensen

Publications and source records attributed to Anders Sorensen.

8 recordsLinked to original sources

arXiv2001

Entanglement and Extreme Spin Squeezing

For any mean value of a cartesian component of a spin vector we identify the smallest possible uncertainty in any of the orthogonal components. The corresponding states are optimal for spectroscopy and atomic clocks. We show that the results for different spin J can be used to identify entanglement and to quantity the depth of entanglement in systems with many particles. With the procedure developed in this letter, collective spin measurements on an ensemble of particles can be used as an experimental proof of multi-particle entanglement

quant-ph↗

arXiv2001

Multi-bit gates for quantum computing

We present a general technique to implement products of many qubit operators communicating via a joint harmonic oscillator degree of freedom in a quantum computer. By conditional displacements and rotations we can implement Hamiltonians which are trigonometric functions of qubit operators. With such operators we can effectively implement higher order gates such as Toffoli gates and C^n-NOT gates, and we show that the entire Grover search algorithm can be implemented in a direct way.

quant-ph↗

arXiv2000

Many-particle entanglement with Bose--Einstein condensates

We propose a method to produce entangled states of several particles starting from a Bose-Einstein condensate. In the proposal, a single fast $π/2$ pulse is applied to the atoms and due to the collisional interaction, the subsequent free time evolution creates an entangled state involving all atoms in the condensate. The created entangled state is a spin-squeezed state which could be used to improve the sensitivity of atomic clocks.

quant-ph↗

arXiv2000

Entanglement and quantum computation with ions in thermal motion

With bichromatic fields it is possible to deterministically produce entangled states of trapped ions. In this paper we present a unified analysis of this process for both weak and strong fields, for slow and fast gates. Simple expressions for the fidelity of creating maximally entangled states of two or an arbitrary number of ions under non-ideal conditions are derived and discussed.

quant-ph↗

arXiv2000

RISQ - reduced instruction set quantum computers

Candidates for quantum computing which offer only restricted control, e.g., due to lack of access to individual qubits, are not useful for general purpose quantum computing. We present concrete proposals for the use of systems with such limitations as RISQ - reduced instruction set quantum computers and devices - for simulation of quantum dynamics, for multi-particle entanglement and squeezing of collective spin variables. These tasks are useful in their own right, and they also provide experimental probes for the functioning of quantum gates in pre-mature proto-types of quantum computers.

quant-ph↗

arXiv1999

Spin-spin interaction and spin-squeezing in an optical lattice

We show that by displacing two optical lattices with respect to each other, we may produce interactions similar to the ones describing ferro-magnetism in condensed matter physics. We also show that particularly simple choices of the interaction lead to spin-squeezing, which may be used to improve the sensitivity of atomic clocks. Spin-squeezing is generated even with partially, and randomly, filled lattices, and our proposal may be implemented with current technology.

quant-ph↗

arXiv1999

Multi-particle entanglement of hot trapped ions

We propose an efficient method to produce multi-particle entangled states of ions in an ion trap for which a wide range of interesting effects and applications have been suggested. Our preparation scheme exploits the collective vibrational motion of the ions, but it works in such a way that this motion need not be fully controlled in the experiment. The ions may, e.g., be in thermal motion and exchange mechanical energy with a surrounding heat bath without detrimental effects on the internal state preparation. Our scheme does not require access to the individual ions in the trap.

quant-ph↗

arXiv1999

Quantum computation with ions in thermal motion

We propose an implementation of quantum logic gates via virtual vibrational excitations in an ion trap quantum computer. Transition paths involving unpopulated, vibrational states interfere destructively to eliminate the dependence of rates and revolution frequencies on vibrational quantum numbers. As a consequence quantum computation becomes feasible with ions whos vibrations are strongly coupled to a thermal reservoir.

quant-ph↗