For instance, the quantum behaviour of these hundred so spin qubits mimicks the behaviour found in numerous mesoscale systems, particularly lattices. In those systems, varying the lattice length and / or other parameters describing the system is often physically impossible or otherwise restrictively difficult, and completely impossible to simulate with a computer. By creating an analogue, pseudo-variations can be performed that give insight into the underlying structure and lead to a better understanding of the original lattice.

From the arXiv paper below the news story: a tunable parameter that mimicks various physical couplings.

That is, by adjusting the single experimental parameter Î¼R we can mimic a continuum of physical couplings including important special cases: a = 0 is infinite range, a = 1 is monopole-monopole (Coulomb-like), a = 2 is monopole-dipole and a = 3 is dipole-dipole. Note that a = 0 results in the so-called JË†z interaction that gives rise to spin-http://sydney.edu.au/news/84.html?newsstoryid=9081

squeezing and is used in quantum logic gates (see Supple-

mentary Information) [27]. In addition, tuning Î¼R also permits

access to both antiferromagnetic (AFM, Î¼R > Ï‰1 ) and ferro-

magnetic (FM, Ï‰2 Î¼R < Ï‰1 ) couplings [13].

"The system we have developed has the potential to perform calculations that would require a supercomputer larger than the size of the known universe - and it does it all in a diameter of less than a millimetre," said Dr Biercuk.Most recent paper from author:

"The projected performance of this new experimental quantum simulator eclipses the current maximum capacity of any known computer by an astonishing 10 to the power of 80. That is 1 followed by 80 zeros, in other words 80 orders of magnitude, a truly mind-boggling scale."

The work smashes previous records in terms of the number of elements working together in a quantum simulator, and therefore the complexity of the problems that can be addressed

http://arxiv.org/abs/1204.5789

## Engineered 2D Ising interactions on a trapped-ion quantum simulator with hundreds of spins

(Submitted on 25 Apr 2012)

The presence of long-range quantum spin correlations underlies a variety of physical phenomena in condensed matter systems, potentially including high-temperature superconductivity. However, many properties of exotic strongly correlated spin systems (e.g., spin liquids) have proved difficult to study, in part because calculations involving N-body entanglement become intractable for as few as N~30 particles. Feynman divined that a quantum simulator - a special-purpose "analog" processor built using quantum particles (qubits) - would be inherently adept at such problems. In the context of quantum magnetism, a number of experiments have demonstrated the feasibility of this approach. However, simulations of quantum magnetism allowing controlled, tunable interactions between spins localized on 2D and 3D lattices of more than a few 10's of qubits have yet to be demonstrated, owing in part to the technical challenge of realizing large-scale qubit arrays. Here we demonstrate a variable-range Ising-type spin-spin interaction J_ij on a naturally occurring 2D triangular crystal lattice of hundreds of spin-1/2 particles (9Be+ ions stored in a Penning trap),a computationally relevant scale more than an order of magnitude larger than existing experiments. We show that a spin-dependent optical dipole force can produce an antiferromagnetic interaction J_ij ~ 1/d_ij^a, where a is tunable over 0<a<3; d_ij is the distance between spin pairs. These power-laws correspond physically to infinite-range (a=0), Coulomb-like (a=1), monopole-dipole (a=2) and dipole-dipole (a=3) couplings. Experimentally, we demonstrate excellent agreement with theory for 0.05<a<1.4.This demonstration coupled with the high spin-count, excellent quantum control and low technical complexity of the Penning trap brings within reach simulation of interesting and otherwise computationally intractable problems in quantum magnetism.