Source code for netket.operator.boson

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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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#    http://www.apache.org/licenses/LICENSE-2.0
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from scipy import sparse as _sparse

from netket.utils.types import DType as _DType

from netket.hilbert import DiscreteHilbert as _DiscreteHilbert

from ._local_operator import LocalOperator as _LocalOperator

# export identity from here as well
from .spin import identity  # noqa: F401


[docs]def destroy( hilbert: _DiscreteHilbert, site: int, dtype: _DType = None ) -> _LocalOperator: """ Builds the boson destruction operator :math:`\\hat{a}` acting on the `site`-th of the Hilbert space `hilbert`. If `hilbert` is a non-Bosonic space of local dimension M, it is considered as a bosonic space of local dimension M. Args: hilbert: The hilbert space. site: The site on which this operator acts. dtype: The datatype to use for the matrix elements. Returns: An instance of {class}`nk.operator.LocalOperator`. """ import numpy as np N = hilbert.size_at_index(site) D = np.array([np.sqrt(m) for m in np.arange(1, N)]) mat = np.diag(D, 1) mat = _sparse.coo_matrix(mat) return _LocalOperator(hilbert, mat, [site], dtype=dtype)
[docs]def create( hilbert: _DiscreteHilbert, site: int, dtype: _DType = float ) -> _LocalOperator: """ Builds the boson creation operator :math:`\\hat{a}^\\dagger` acting on the `site`-th of the Hilbert space `hilbert`. If `hilbert` is a non-Bosonic space of local dimension M, it is considered as a bosonic space of local dimension M. Args: hilbert: The hilbert space. site: The site on which this operator acts. dtype: The datatype to use for the matrix elements. Returns: An instance of {class}`nk.operator.LocalOperator`. """ import numpy as np N = hilbert.size_at_index(site) D = np.array([np.sqrt(m) for m in np.arange(1, N)]) mat = np.diag(D, -1) mat = _sparse.coo_matrix(mat) return _LocalOperator(hilbert, mat, [site], dtype=dtype)
[docs]def number( hilbert: _DiscreteHilbert, site: int, dtype: _DType = float ) -> _LocalOperator: """ Builds the number operator :math:`\\hat{a}^\\dagger\\hat{a}` acting on the `site`-th of the Hilbert space `hilbert`. If `hilbert` is a non-Bosonic space of local dimension M, it is considered as a bosonic space of local dimension M. Args: hilbert: The hilbert space. site: The site on which this operator acts. dtype: The datatype to use for the matrix elements. Returns: An instance of {class}`nk.operator.LocalOperator`. """ import numpy as np N = hilbert.size_at_index(site) D = np.array([m for m in np.arange(0, N)]) mat = np.diag(D, 0) mat = _sparse.coo_matrix(mat) return _LocalOperator(hilbert, mat, [site], dtype=dtype)
[docs]def proj( hilbert: _DiscreteHilbert, site: int, n: int, dtype: _DType = float ) -> _LocalOperator: """ Builds the projector operator :math:`|n\\rangle\\langle n |` acting on the `site`-th of the Hilbert space `hilbert` and collapsing on the state with `n` bosons. If `hilbert` is a non-Bosonic space of local dimension M, it is considered as a bosonic space of local dimension M. Args: hilbert: The hilbert space. site: The site on which this operator acts. dtype: The datatype to use for the matrix elements. Returns: An instance of {class}`nk.operator.LocalOperator`. """ import numpy as np N = hilbert.size_at_index(site) if n >= N: raise ValueError("Cannot project on a state above the cutoff.") D = np.array([0 for m in np.arange(0, N)]) D[n] = 1 mat = np.diag(D, 0) mat = _sparse.coo_matrix(mat) return _LocalOperator(hilbert, mat, [site], dtype=dtype)