hqs_quantum_solver.spin_util#

Utility functions for working with spin systems.

Functions

class SpinState#

The two states of a spin-½ particle.

DOWN = 1#

‘Down’ spin state.

UP = 2#

‘Up’ spin state.

pure_spin_state(spins: list[SpinState], Sz: int | None = None, mod_Sz: int = 2, dtype: type = np.complex128) → ndarray#

Create a representation of a pure spin state for a system of spin-½ particles.

Given a list of single-spin states, i.e., ${\sigma }_i\in \{\downarrow ,\uparrow \}$ for $i=0,\dots ,n-1$, this function returns a representation of the state

$$|{\sigma }_0{\sigma }_1\cdots {\sigma }_{n-1}⟩=|{\sigma }_0⟩\otimes |{\sigma }_1⟩\otimes \cdots \otimes |{\sigma }_{n-1}⟩.$$

Warning

The values of Sz and mod_Sz need to be the same as in the construction of the operator that this state vector should be used with.

Warning

This class is deprecated. Use the hqs_quantum_solver.spins.VectorSpace.fock_state() instead.

Parameters:

• spins (list[SpinState]) – The list of single-particle spin states.

• Sz (Optional[int]) – The total spin polarization in the z-axis, Sz, in units of ħ/2. abs(Sz) must be less than or equal to the number of sites.

• mod_Sz (int) – Integer representing the extent of Sz violations allowed (in modular arithmetic).

• dtype (type) – The datatype of the state vector to be returned.

Returns:

The state vector.

Return type:

ndarray