System

System(
    label=None,
    num_states=1,
    energies=None,
    decays=None,
    initial_state=None,
    fields=None,
)

An open quantum system: its states, decays and the fields coupling them.

The system can be an atom or any other few-level quantum system, such as a quantum dot or a colour centre.

Parameters

Name	Type	Description	Default
label	str \| None	string label describing the system.	`None`
num_states	int	number of states.	`1`
energies	list[float] \| None	absolute or relative energy levels of the states.	`None`
decays	list[dict] \| None	list of dicts representing decays. e.g. [ { “rate”: 1.0, “channels”: [[0,1]], “factors”: [1.0] } { “rate”: 2.0, “channels”: [[2,1], [3,1]], “factors”: [0.707, 0.707] } ]	`None`
initial_state	list[float] \| None	initial state, as a list or array	`None`
fields	list[dict] \| None	list of dicts representing the fields that couple the system’s states.	`None`

Name	Description
add_field	Add a Field to the list given a dict representing the field.
build_fields	Build the field list given a list of dicts representing fields.
build_initial_state	Build the initial density matrix for the system.
build_operators	Build the quantum operators representing the bare Hamiltonian,
get_detunings	Returns a list of detunings, one for each field in fields.
get_fields_sum_coherence	Returns the sum coherences of the system density matrix for each
set_H_Delta	Set the detuning part of the interaction Hamiltonian, H_Delta,
set_H_Omega	Set the Rabi frequency part of the interaction Hamiltonian.
to_json_str	Return a JSON string representation of the System object.

System.add_field(field_dict)

Add a Field to the list given a dict representing the field.

System.build_fields(field_dicts)

Build the field list given a list of dicts representing fields.

System.build_initial_state(initial_state=None)

Build the initial density matrix for the system.

The default is for all of the population to be in |0><0|.

Name	Type	Description	Default
initial_state	list[float] \| None	a list or array of populations, length num_states. If not given, all the population starts in level 0.	`None`

Name	Type	Description
	qu.Qobj	The initial density matrix, diagonal with the given populations.
	qu.Qobj	It is also stored as `self.initial_state` and `self.rho`.

Name	Type	Description
	ValueError	If `initial_state` has the wrong length or its elements do not sum to 1.

System.build_operators()

Build the quantum operators representing the bare Hamiltonian, collapse operators and interaction Hamiltonian.

System.get_detunings()

Returns a list of detunings, one for each field in fields.

System.get_fields_sum_coherence(states_t=None)

Returns the sum coherences of the system density matrix for each field, including the relative strength factors.

Name	Type	Description	Default
states_t	np.ndarray \| None	(optional) a states_t object. If not provided, use self.states_t()	`None`

Name	Type	Description
	np.ndarray	np.ndarray of shape (num_fields, t_steps+1)

System.set_H_Delta(detunings)

Set the detuning part of the interaction Hamiltonian, H_Delta, given a list of detunings.

Name	Type	Description	Default
detunings	list[float]	list of floats: detunings of each field in the list	required

System.set_H_Omega(rabi_freqs, rabi_freq_t_funcs, rabi_freq_t_args)

Set the Rabi frequency part of the interaction Hamiltonian.

Updates each field’s Rabi frequency and time function, then rebuilds the Hamiltonian.

Name	Type	Description	Default
rabi_freqs	list[float]	Rabi frequency for each field.	required
rabi_freq_t_funcs	list	Name of the time function for each field, as in `clerq.t_funcs` (e.g. `"gaussian"`).	required
rabi_freq_t_args	list[dict]	Argument dict for each field’s time function.	required

Name	Type	Description
	list	The list of Rabi frequency Hamiltonian terms, one for each field.

System.to_json_str()

Return a JSON string representation of the System object.

Name	Type	Description
	str	(string) JSON representation of the System object.