Not for QMC and long times, since the real time evolution gives complex phases in the weights.

Matthias

On 3 Aug 2011, at 11:16, Dan Thompson wrote:

I think I understand what you mean now. It isn't possible to simulate a dynamic hamiltonian with alps. Ie., a MC time-dependent hamiltonian. -Dan

On Wed, Aug 3, 2011 at 1:39 PM, Matthias Troyer troyer@phys.ethz.ch wrote: Hi Dan,

That only makes sense if you are interested in the efficiency of our QMC algorithms. But the annealing time T in this scheme has nothing do to with real time.

Matthias

On 3 Aug 2011, at 10:37, Dan Thompson wrote:

...

Hey Matthias,

Thanks for the quick reply. Here's what I'm trying to do with the alps qmc code:

• Initially, I want to start with a quantum spin 1/2 system in a strong, transverse magnetic field. It should be in the ground state of this particular hamiltonian.
• Then, the idea is to simulataneously:

a) turn off the transverse field b) turn on a field along the spin axis and c) turn on couplings between the various spins. This would be the quantum annealing part and should take T MC time.

• After the annealing, I would measure the new state of the spin system. Namely, I would look at the fidelity of this state and the ground state of the hamiltonian with the couplings and field along the spin axis.

Does that make more sense? The idea would be to measure how the fidelity changes as the annealing time T changes.

Cheers, -Dan

On Wed, Aug 3, 2011 at 12:50 PM, Matthias Troyer troyer@phys.ethz.ch wrote:

On 3 Aug 2011, at 09:40, Dan Thompson wrote:

...

Hello,

I was just wondering if there was a way to simulate the quantum annealing of a spin chain/lattice. Namely, adjust the parameters in a model file so that over the course of the quantum monte carlo simulation I could start with one hamiltonian (a simple heisenberg hamiltonian with nearest neighbour couplings and a transverse magnetic field) and finish with a different one (transverse field turned off).

Cheers, -Dan

Hi Dan,

What is the purpose of this? Do you want to use it to improve the simulation or to get some time-dependent measurements? The QMC codes only measure equilibrium properties at the given parameters and you can thus just do a series of simulations. Please remember that MC time and real time are not the same.

Matthias