Fock States#
Warning
The ordering of the Fock basis is increasing with particle numbers, and in each particle number conserving subspace, lexicographic ordering is used.
Example for 3 modes:
General Fock State#
- class FockState(*, d: int, calculator: BaseCalculator, config: Config | None = None)#
Object to represent a general bosonic state in the Fock basis.
Note
If you only work with pure states, it is advised to use
PureFockState
instead.- Parameters:
d (int) – The number of modes.
calculator (BaseCalculator) – Instance containing calculation functions.
config (Config) – Instance containing constants for the simulation.
- classmethod from_fock_state(state: BaseFockState) FockState #
Instantiation using another
BaseFockState
instance.- Parameters:
state (BaseFockState) – The instance from which a
FockState
instance is created.
- property nonzero_elements: Generator[Tuple[complex, Tuple], Any, None]#
The nonzero contributions to the state representation in Fock basis.
- property density_matrix: ndarray#
The density matrix of the state in terms of the Fock basis vectors.
- get_particle_detection_probability(occupation_number: ndarray) float #
Returns the particle number detection probability using the occupation number specified as a parameter.
- property fock_probabilities: ndarray#
Returns the particle detection probabilities.
Note
The ordering of the Fock basis is increasing with particle numbers, and in each particle number conserving subspace, lexicographic ordering is used.
- Returns:
The particle detection probabilities.
- Return type:
- property fock_probabilities_map: Dict[Tuple[int, ...], float]#
The particle number detection probabilities in a map.
- reduced(modes: Tuple[int, ...]) FockState #
Reduces the state to a subsystem corresponding to the specified modes.
- normalize() None #
Normalizes the density matrix to have a trace of 1.
- Raises:
RuntimeError – Raised if the current norm of the state is too close to 0.
- validate() None #
Validates the represented state.
- Raises:
InvalidState – Raised, if the density matrix is not positive semidefinite, not self-adjoint or the trace of the density matrix is not 1.
- quadratures_mean_variance(modes: Tuple[int, ...], phi: float = 0) Tuple[float, float] #
This method calculates the mean and the variance of the qudrature operators for a single qumode state. The quadrature operators \(x\) and \(p\) for a mode \(i\) can be calculated using the creation and annihilation operators as follows:
\[\begin{split}x_i &= \sqrt{\frac{\hbar}{2}} (a_i + a_i^\dagger) \\ p_i &= -i \sqrt{\frac{\hbar}{2}} (a_i - a_i^\dagger).\end{split}\]Let \(\phi \in [ 0, 2 \pi )\), we can rotate the quadratures using the following transformation:
\[Q_{i, \phi} = \cos\phi~x_i + \sin\phi~p_i.\]The expectation value \(\langle Q_{i, \phi}\rangle\) can be calculated as:
\[\operatorname{Tr}(\rho_i Q_{i, \phi}),\]where \(\rho_i\) is the reduced density matrix of the mode \(i\) and \(Q_{i, \phi}\) is the rotated quadrature operator for a single mode and the variance is calculated as:
\[\operatorname{\textit{Var}(Q_{i,\phi})} = \langle Q_{i, \phi}^{2}\rangle - \langle Q_{i, \phi}\rangle^{2}.\]- Parameters:
phi (float) – The rotation angle. By default it is 0 which means that the mean of the position operator is being calculated. For \(\phi= \frac{\pi}{2}\) the mean of the momentum operator is being calculated.
modes (tuple[int]) – The correspoding mode at which the mean of the quadratures are being calculated.
- Returns:
- A tuple that contains the expectation value and the
varianceof of the quadrature operator respectively.
- Return type:
Pure Fock State#
- class PureFockState(*, d: int, calculator: BaseCalculator, config: Config | None = None)#
A simulated pure Fock state.
If no mixed states are needed for a Fock simulation, then this state is the most appropriate currently, since it does not store an entire density matrix, only a state vector with size
\[{d + c - 1 \choose c - 1},\]where \(c \in \mathbb{N}\) is the Fock space cutoff.
- Variables:
state_vector – The state vector of the quantum state.
- Parameters:
d (int) – The number of modes.
calculator (BaseCalculator) – Instance containing calculation functions.
config (Config) – Instance containing constants for the simulation.
- property nonzero_elements#
The nonzero contributions to the state representation in Fock basis.
- property density_matrix: ndarray#
The density matrix of the state in terms of the Fock basis vectors.
- reduced(modes: Tuple[int, ...]) FockState #
Reduces the state to a subsystem corresponding to the specified modes.
- get_particle_detection_probability(occupation_number: ndarray) float #
Returns the particle number detection probability using the occupation number specified as a parameter.
- property fock_probabilities: ndarray#
Returns the particle detection probabilities.
Note
The ordering of the Fock basis is increasing with particle numbers, and in each particle number conserving subspace, lexicographic ordering is used.
- Returns:
The particle detection probabilities.
- Return type:
- property fock_probabilities_map: Dict[Tuple[int, ...], float]#
The particle number detection probabilities in a map.
- validate() None #
Validates the represented state.
- Raises:
InvalidState – Raised, if the norm of the state vector is not close to 1.0.
- quadratures_mean_variance(modes: Tuple[int, ...], phi: float = 0) Tuple[float, float] #
This method calculates the mean and the variance of the qudrature operators for a single qumode state. The quadrature operators \(x\) and \(p\) for a mode \(i\) can be calculated using the creation and annihilation operators as follows:
\[\begin{split}x_i &= \sqrt{\frac{\hbar}{2}} (a_i + a_i^\dagger) \\ p_i &= -i \sqrt{\frac{\hbar}{2}} (a_i - a_i^\dagger).\end{split}\]Let \(\phi \in [ 0, 2 \pi )\), we can rotate the quadratures using the following transformation:
\[Q_{i, \phi} = \cos\phi~x_i + \sin\phi~p_i.\]The expectation value \(\langle Q_{i, \phi}\rangle\) can be calculated as:
\[\operatorname{Tr}(\rho_i Q_{i, \phi}),\]where \(\rho_i\) is the reduced density matrix of the mode \(i\) and \(Q_{i, \phi}\) is the rotated quadrature operator for a single mode and the variance is calculated as:
\[\operatorname{\textit{Var}(Q_{i,\phi})} = \langle Q_{i, \phi}^{2}\rangle - \langle Q_{i, \phi}\rangle^{2}.\]- Parameters:
phi (float) – The rotation angle. By default it is 0 which means that the mean of the position operator is being calculated. For \(\phi= \frac{\pi}{2}\) the mean of the momentum operator is being calculated.
modes (tuple[int]) – The correspoding mode at which the mean of the quadratures are being calculated.
- Returns:
- A tuple that contains the expectation value and the
varianceof of the quadrature operator respectively.
- Return type: