Source code for sympy.physics.quantum.hilbert

"""Hilbert spaces for quantum mechanics.

Authors:
* Brian Granger
* Matt Curry
"""

from sympy import Basic, Interval, oo, sympify
from sympy.printing.pretty.stringpict import prettyForm

from sympy.physics.quantum.qexpr import QuantumError

from sympy.core.compatibility import reduce
from functools import reduce

__all__ = [
    'HilbertSpaceError',
    'HilbertSpace',
    'ComplexSpace',
    'L2',
    'FockSpace'
]

#-----------------------------------------------------------------------------
# Main objects
#-----------------------------------------------------------------------------

class HilbertSpaceError(QuantumError):
    pass

#-----------------------------------------------------------------------------
# Main objects
#-----------------------------------------------------------------------------

[docs]class HilbertSpace(Basic): """An abstract Hilbert space for quantum mechanics. In short, a Hilbert space is an abstract vector space that is complete with inner products defined [1]_. Examples ======== >>> from sympy.physics.quantum.hilbert import HilbertSpace >>> hs = HilbertSpace() >>> hs H References ========== .. [1] http://en.wikipedia.org/wiki/Hilbert_space """ def __new__(cls): obj = Basic.__new__(cls) return obj @property
[docs] def dimension(self): """Return the Hilbert dimension of the space.""" raise NotImplementedError('This Hilbert space has no dimension.')
def __add__(self, other): return DirectSumHilbertSpace(self, other) def __radd__(self, other): return DirectSumHilbertSpace(other, self) def __mul__(self, other): return TensorProductHilbertSpace(self, other) def __rmul__(self, other): return TensorProductHilbertSpace(other, self) def __pow__(self, other, mod=None): if mod is not None: raise ValueError('The third argument to __pow__ is not supported\ for Hilbert spaces.') return TensorPowerHilbertSpace(self, other) def __contains__(self, other): """Is the operator or state in this Hilbert space. This is checked by comparing the classes of the Hilbert spaces, not the instances. This is to allow Hilbert Spaces with symbolic dimensions. """ if other.hilbert_space.__class__ == self.__class__: return True else: return False def _sympystr(self, printer, *args): return 'H' def _pretty(self, printer, *args): # u = u'\u2108' # script u = '\u0048' return prettyForm(u) def _latex(self, printer, *args): return r'\mathcal{H}'
[docs]class ComplexSpace(HilbertSpace): """Finite dimensional Hilbert space of complex vectors. The elements of this Hilbert space are n-dimensional complex valued vectors with the usual inner product that takes the complex conjugate of the vector on the right. A classic example of this type of Hilbert space is spin-1/2, which is ``ComplexSpace(2)``. Generalizing to spin-s, the space is ``ComplexSpace(2*s+1)``. Quantum computing with N qubits is done with the direct product space ``ComplexSpace(2)**N``. Examples ======== >>> from sympy import symbols >>> from sympy.physics.quantum.hilbert import ComplexSpace >>> c1 = ComplexSpace(2) >>> c1 C(2) >>> c1.dimension 2 >>> n = symbols('n') >>> c2 = ComplexSpace(n) >>> c2 C(n) >>> c2.dimension n """ def __new__(cls, dimension): dimension = sympify(dimension) r = cls.eval(dimension) if isinstance(r, Basic): return r obj = Basic.__new__(cls, dimension) return obj @classmethod def eval(cls, dimension): if len(dimension.atoms()) == 1: if not (dimension.is_Integer and dimension > 0 or dimension is oo\ or dimension.is_Symbol): raise TypeError('The dimension of a ComplexSpace can only' 'be a positive integer, oo, or a Symbol: %r' \ % dimension) else: for dim in dimension.atoms(): if not (dim.is_Integer or dim is oo or dim.is_Symbol): raise TypeError('The dimension of a ComplexSpace can only' ' contain integers, oo, or a Symbol: %r' \ % dim) @property def dimension(self): return self.args[0] def _sympyrepr(self, printer, *args): return "%s(%s)" % (self.__class__.__name__, printer._print(self.dimension, *args)) def _sympystr(self, printer, *args): return "C(%s)" % printer._print(self.dimension, *args) def _pretty(self, printer, *args): # u = u'\u2102' # script u = '\u0043' pform_exp = printer._print(self.dimension, *args) pform_base = prettyForm(u) return pform_base**pform_exp def _latex(self, printer, *args): return r'\mathcal{C}^{%s}' % printer._print(self.dimension, *args)
[docs]class L2(HilbertSpace): """The Hilbert space of square integrable functions on an interval. An L2 object takes in a single sympy Interval argument which represents the interval its functions (vectors) are defined on. Examples ======== >>> from sympy import Interval, oo >>> from sympy.physics.quantum.hilbert import L2 >>> hs = L2(Interval(0,oo)) >>> hs L2([0, oo)) >>> hs.dimension oo >>> hs.interval [0, oo) """ def __new__(cls, interval): if not isinstance(interval, Interval): raise TypeError('L2 interval must be an Interval instance: %r'\ % interval) obj = Basic.__new__(cls, interval) return obj @property def dimension(self): return oo @property def interval(self): return self.args[0] def _sympyrepr(self, printer, *args): return "L2(%s)" % printer._print(self.interval, *args) def _sympystr(self, printer, *args): return "L2(%s)" % printer._print(self.interval, *args) def _pretty(self, printer, *args): pform_exp = prettyForm("2") pform_base = prettyForm("L") return pform_base**pform_exp def _latex(self, printer, *args): interval = printer._print(self.interval, *args) return r'{\mathcal{L}^2}\left( %s \right)' % interval
[docs]class FockSpace(HilbertSpace): """The Hilbert space for second quantization. Technically, this Hilbert space is a infinite direct sum of direct products of single particle Hilbert spaces [1]_. This is a mess, so we have a class to represent it directly. Examples ======== >>> from sympy.physics.quantum.hilbert import FockSpace >>> hs = FockSpace() >>> hs F >>> hs.dimension oo References ========== .. [1] http://en.wikipedia.org/wiki/Fock_space """ def __new__(cls): obj = Basic.__new__(cls) return obj @property def dimension(self): return oo def _sympyrepr(self, printer, *args): return "FockSpace()" def _sympystr(self, printer, *args): return "F" def _pretty(self, printer, *args): # u = u'\u2131' # script u = '\u0046' return prettyForm(u) def _latex(self, printer, *args): return r'\mathcal{F}'
class TensorProductHilbertSpace(HilbertSpace): """A tensor product of Hilbert spaces [1]_. The tensor product between Hilbert spaces is represented by the operator ``*`` Products of the same Hilbert space will be combined into tensor powers. A ``TensorProductHilbertSpace`` object takes in an arbitrary number of ``HilbertSpace`` objects as its arguments. In addition, multiplication of ``HilbertSpace`` objects will automatically return this tensor product object. Examples ======== >>> from sympy.physics.quantum.hilbert import ComplexSpace, FockSpace >>> from sympy import symbols >>> c = ComplexSpace(2) >>> f = FockSpace() >>> hs = c*f >>> hs C(2)*F >>> hs.dimension oo >>> hs.spaces (C(2), F) >>> c1 = ComplexSpace(2) >>> n = symbols('n') >>> c2 = ComplexSpace(n) >>> hs = c1*c2 >>> hs C(2)*C(n) >>> hs.dimension 2*n References ========== .. [1] http://en.wikipedia.org/wiki/Hilbert_space#Tensor_products """ def __new__(cls, *args): r = cls.eval(args) if isinstance(r, Basic): return r obj = Basic.__new__(cls, *args) return obj @classmethod def eval(cls, args): """Evaluates the direct product.""" new_args = [] recall = False #flatten arguments for arg in args: if isinstance(arg, TensorProductHilbertSpace): new_args.extend(arg.args) recall = True elif isinstance(arg, (HilbertSpace, TensorPowerHilbertSpace)): new_args.append(arg) else: raise TypeError('Hilbert spaces can only be multiplied by\ other Hilbert spaces: %r' % arg) #combine like arguments into direct powers comb_args = [] prev_arg = None for new_arg in new_args: if prev_arg != None: if isinstance(new_arg, TensorPowerHilbertSpace) and\ isinstance(prev_arg, TensorPowerHilbertSpace) and\ new_arg.base == prev_arg.base: prev_arg = new_arg.base**(new_arg.exp+prev_arg.exp) elif isinstance(new_arg, TensorPowerHilbertSpace) and\ new_arg.base == prev_arg: prev_arg = prev_arg**(new_arg.exp+1) elif isinstance(prev_arg, TensorPowerHilbertSpace) and\ new_arg == prev_arg.base: prev_arg = new_arg**(prev_arg.exp+1) elif new_arg == prev_arg: prev_arg = new_arg**2 else: comb_args.append(prev_arg) prev_arg = new_arg elif prev_arg == None: prev_arg = new_arg comb_args.append(prev_arg) if recall: return TensorProductHilbertSpace(*comb_args) elif len(comb_args) == 1: return TensorPowerHilbertSpace(comb_args[0].base, comb_args[0].exp) else: return None @property def dimension(self): arg_list = [arg.dimension for arg in self.args] if oo in arg_list: return oo else: return reduce(lambda x,y: x*y, arg_list) @property def spaces(self): """A tuple of the Hilbert spaces in this tensor product.""" return self.args def _spaces_printer(self, printer, *args): spaces_strs = [] for arg in self.args: s = printer._print(arg, *args) if isinstance(arg, DirectSumHilbertSpace): s = '(%s)' % s spaces_strs.append(s) return spaces_strs def _sympyrepr(self, printer, *args): spaces_reprs = self._spaces_printer(printer, *args) return "TensorProductHilbertSpace(%s)" % ','.join(spaces_reprs) def _sympystr(self, printer, *args): spaces_strs = self._spaces_printer(printer, *args) return '*'.join(spaces_strs) def _pretty(self, printer, *args): length = len(self.args) pform = printer._print('', *args) for i in range(length): next_pform = printer._print(self.args[i], *args) if isinstance(self.args[i], (DirectSumHilbertSpace, TensorProductHilbertSpace)): next_pform = prettyForm( *next_pform.parens(left='(', right=')') ) pform = prettyForm(*pform.right(next_pform)) if i != length-1: if printer._use_unicode: pform = prettyForm(*pform.right(' ' + '\u2a02' + ' ')) else: pform = prettyForm(*pform.right(' x ')) return pform def _latex(self, printer, *args): length = len(self.args) s = '' for i in range(length): arg_s = printer._print(self.args[i], *args) if isinstance(self.args[i], (DirectSumHilbertSpace, TensorProductHilbertSpace)): arg_s = r'\left(%s\right)' % arg_s s = s + arg_s if i != length-1: s = s + r'\otimes ' return s class DirectSumHilbertSpace(HilbertSpace): """A direct sum of Hilbert spaces [1]_. This class uses the ``+`` operator to represent direct sums between different Hilbert spaces. A ``DirectSumHilbertSpace`` object takes in an arbitrary number of ``HilbertSpace`` objects as its arguments. Also, addition of ``HilbertSpace`` objects will automatically return a direct sum object. Examples ======== >>> from sympy.physics.quantum.hilbert import ComplexSpace, FockSpace >>> from sympy import symbols >>> c = ComplexSpace(2) >>> f = FockSpace() >>> hs = c+f >>> hs C(2)+F >>> hs.dimension oo >>> list(hs.spaces) [C(2), F] References ========== .. [1] http://en.wikipedia.org/wiki/Hilbert_space#Direct_sums """ def __new__(cls, *args): r = cls.eval(args) if isinstance(r, Basic): return r obj = Basic.__new__(cls, *args) return obj @classmethod def eval(cls, args): """Evaluates the direct product.""" new_args = [] recall = False #flatten arguments for arg in args: if isinstance(arg, DirectSumHilbertSpace): new_args.extend(arg.args) recall = True elif isinstance(arg, HilbertSpace): new_args.append(arg) else: raise TypeError('Hilbert spaces can only be summed with other\ Hilbert spaces: %r' % arg) if recall: return DirectSumHilbertSpace(*new_args) else: return None @property def dimension(self): arg_list = [arg.dimension for arg in self.args] if oo in arg_list: return oo else: return reduce(lambda x,y: x+y, arg_list) @property def spaces(self): """A tuple of the Hilbert spaces in this direct sum.""" return self.args def _sympyrepr(self, printer, *args): spaces_reprs = [printer._print(arg, *args) for arg in self.args] return "DirectSumHilbertSpace(%s)" % ','.join(spaces_reprs) def _sympystr(self, printer, *args): spaces_strs = [printer._print(arg, *args) for arg in self.args] return '+'.join(spaces_strs) def _pretty(self, printer, *args): length = len(self.args) pform = printer._print('', *args) for i in range(length): next_pform = printer._print(self.args[i], *args) if isinstance(self.args[i], (DirectSumHilbertSpace, TensorProductHilbertSpace)): next_pform = prettyForm( *next_pform.parens(left='(', right=')') ) pform = prettyForm(*pform.right(next_pform)) if i != length-1: if printer._use_unicode: pform = prettyForm(*pform.right(' ' + '\u2295' + ' ')) else: pform = prettyForm(*pform.right(' + ')) return pform def _latex(self, printer, *args): length = len(self.args) s = '' for i in range(length): arg_s = printer._print(self.args[i], *args) if isinstance(self.args[i], (DirectSumHilbertSpace, TensorProductHilbertSpace)): arg_s = r'\left(%s\right)' % arg_s s = s + arg_s if i != length-1: s = s + r'\oplus ' return s class TensorPowerHilbertSpace(HilbertSpace): """An exponentiated Hilbert space [1]_. Tensor powers (repeated tensor products) are represented by the operator ``**`` Identical Hilbert spaces that are multiplied together will be automatically combined into a single tensor power object. Any Hilbert space, product, or sum may be raised to a tensor power. The ``TensorPowerHilbertSpace`` takes two arguments: the Hilbert space; and the tensor power (number). Examples ======== >>> from sympy.physics.quantum.hilbert import ComplexSpace, FockSpace >>> from sympy import symbols >>> n = symbols('n') >>> c = ComplexSpace(2) >>> hs = c**n >>> hs C(2)**n >>> hs.dimension 2**n >>> c = ComplexSpace(2) >>> c*c C(2)**2 >>> f = FockSpace() >>> c*f*f C(2)*F**2 References ========== .. [1] http://en.wikipedia.org/wiki/Hilbert_space#Tensor_products """ def __new__(cls, *args): r = cls.eval(args) if isinstance(r, Basic): return r return Basic.__new__(cls, *r) @classmethod def eval(cls, args): new_args = args[0], sympify(args[1]) exp = new_args[1] #simplify hs**1 -> hs if exp == 1: return args[0] #simplify hs**0 -> 1 if exp == 0: return sympify(1) #check (and allow) for hs**(x+42+y...) case if len(exp.atoms()) == 1: if not (exp.is_Integer and exp >= 0 or exp.is_Symbol): raise ValueError('Hilbert spaces can only be raised to\ positive integers or Symbols: %r' % exp) else: for power in exp.atoms(): if not (power.is_Integer or power.is_Symbol): raise ValueError('Tensor powers can only contain integers\ or Symbols: %r' % power) return new_args @property def base(self): return self.args[0] @property def exp(self): return self.args[1] @property def dimension(self): if self.base.dimension == oo: return oo else: return self.base.dimension**self.exp def _sympyrepr(self, printer, *args): return "TensorPowerHilbertSpace(%s,%s)" % (printer._print(self.base,\ *args), printer._print(self.exp, *args)) def _sympystr(self, printer, *args): return "%s**%s" % (printer._print(self.base, *args),\ printer._print(self.exp, *args)) def _pretty(self, printer, *args): pform_exp = printer._print(self.exp, *args) if printer._use_unicode: pform_exp = prettyForm(*pform_exp.left(prettyForm('\u2a02'))) else: pform_exp = prettyForm(*pform_exp.left(prettyForm('x'))) pform_base = printer._print(self.base, *args) return pform_base**pform_exp def _latex(self, printer, *args): base = printer._print(self.base, *args) exp = printer._print(self.exp, *args) return r'{%s}^{\otimes %s}' % (base, exp)