Time-dependent variational Monte Carlo explained
The time-dependent variational Monte Carlo (t-VMC) method is a quantum Monte Carlo approach to study the dynamics of closed, non-relativistic quantum systems in the context of the quantum many-body problem. It is an extension of the variational Monte Carlo method, in which a time-dependent pure quantum state is encoded by some variational wave function, generally parametrized as
\Psi(X,t)=\exp\left(\sumkak(t)Ok(X)\right)
where the complex-valued
are time-dependent variational parameters,
denotes a many-body configuration and
are time-independent operators that define the specific
ansatz. The time evolution of the parameters
can be found upon imposing a
variational principle to the
wave function. In particular one can show that the optimal parameters for the evolution satisfy at each time the equation of motion
where
is the
Hamiltonian of the system,
\langleAB
AB\ranglet-\langleA\ranglet\langleB\ranglet
are connected averages, and the quantum expectation values are taken over the time-dependent variational
wave function, i.e.,
\langle … \ranglet\equiv\langle\Psi(t)| … |\Psi(t)\rangle
.
In analogy with the Variational Monte Carlo approach and following the Monte Carlo method for evaluating integrals, we can interpret
| |\Psi(X,t)|2 |
\int|\Psi(X,t)|2dX |
as a
probability distribution function over the multi-dimensional space spanned by the many-body configurations
. The
Metropolis–Hastings algorithm is then used to sample exactly from this probability distribution and, at each time
, the quantities entering the equation of motion are evaluated as statistical averages over the sampled configurations. The trajectories
of the variational parameters are then found upon numerical integration of the associated
differential equation.
References
- G. Carleo . F. Becca . M. Schiró . M. Fabrizio . amp . 2012 . Localization and glassy dynamics of many-body quantum systems . Sci. Rep. . 2 . 243 . 10.1038/srep00243 . 22355756 . 3272662 . 1109.2516 . 2012NatSR...2E.243C .
- G. Carleo . F. Becca . L. Sanchez-Palencia . S. Sorella . M. Fabrizio . amp . Light-cone effect and supersonic correlations in one- and two-dimensional bosonic superfluids . Phys. Rev. A . 89 . 3 . 031602(R) . 10.1103/PhysRevA.89.031602 . 2014. 1310.2246 . 2014PhRvA..89c1602C . 45660254 .
- G. Carleo . Spectral and dynamical properties of strongly correlated systems . PhD Thesis . 107–128 . 2011. 20.500.11767/4289 .