pygsti.models.explicitmodel

Defines the ExplicitOpModel class and supporting functionality.

Module Contents

Classes

ExplicitOpModel	Encapsulates a set of gate, state preparation, and POVM effect operations.
ExplicitLayerRules	Rule: layer must appear explicitly as a "primitive op"

class pygsti.models.explicitmodel.ExplicitOpModel(state_space, basis='pp', default_gate_type='full', default_prep_type='auto', default_povm_type='auto', default_instrument_type='auto', prep_prefix='rho', effect_prefix='E', gate_prefix='G', povm_prefix='M', instrument_prefix='I', simulator='auto', evotype='default')

Bases: pygsti.models.model.OpModel

Encapsulates a set of gate, state preparation, and POVM effect operations.

An ExplictOpModel stores a set of labeled LinearOperator objects and provides dictionary-like access to their matrices. State preparation and POVM effect operations are represented as column vectors.

Parameters

state_spaceStateSpace

The state space for this model.

basis{“pp”,”gm”,”qt”,”std”,”sv”} or Basis, optional

The basis used for the state space by dense superoperator representations.

default_param{“full”, “TP”, “CPTP”, etc.}, optional

Specifies the default gate and SPAM vector parameterization type. Can be any value allowed by set_all_parameterizations(), which also gives a description of each parameterization type.

prep_prefix: string, optional

Key prefixe for state preparations, allowing the model to determing what type of object a key corresponds to.

effect_prefixstring, optional

Key prefix for POVM effects, allowing the model to determing what type of object a key corresponds to.

gate_prefixstring, optional

Key prefix for gates, allowing the model to determing what type of object a key corresponds to.

povm_prefixstring, optional

Key prefix for POVMs, allowing the model to determing what type of object a key corresponds to.

instrument_prefixstring, optional

Key prefix for instruments, allowing the model to determing what type of object a key corresponds to.

simulatorForwardSimulator or {“auto”, “matrix”, “map”}

The circuit simulator used to compute any requested probabilities, e.g. from probs() or bulk_probs(). The default value of “auto” automatically selects the simulation type, and is usually what you want. Other special allowed values are:

• “matrix” : op_matrix-op_matrix products are computed and cached to get composite gates which can then quickly simulate a circuit for any preparation and outcome. High memory demand; best for a small number of (1 or 2) qubits.

• “map” : op_matrix-state_vector products are repeatedly computed to simulate circuits. Slower for a small number of qubits, but faster and more memory efficient for higher numbers of qubits (3+).

evotypeEvotype or str, optional

The evolution type of this model, describing how states are represented. The special value “default” is equivalent to specifying the value of pygsti.evotypes.Evotype.default_evotype.

Creates a new OpModel. Rarely used except from derived classes __init__ functions.

property default_gauge_group

Gets the default gauge group for performing gauge transformations on this Model.

Returns

GaugeGroup

property prep

The unique state preparation in this model, if one exists.

If not, a ValueError is raised.

Returns

State

property effects

The effect vectors from the unique POVM in this model, if one exists.

If not, a ValueError is raised.

Returns

list of POVMEffects

property num_elements

Return the number of total operation matrix and spam vector elements in this model.

This is in general different from the number of parameters in the model, which are the number of free variables used to generate all of the matrix and vector elements.

Returns

int

the number of model elements.

property num_nongauge_params

Return the number of non-gauge parameters in this model.

Returns

int

the number of non-gauge model parameters.

property num_gauge_params

Return the number of gauge parameters in this model.

Returns

int

the number of gauge model parameters.

convert_members_inplace(to_type, categories_to_convert='all', labels_to_convert='all', ideal_model=None, flatten_structure=False, set_default_gauge_group=False, cptp_truncation_tol=1e-06)

TODO: docstring – like set_all_parameterizations but doesn’t set default gauge group by default

set_default_gauge_group_for_member_type(member_type)

TODO: docstring

set_all_parameterizations(gate_type, prep_type='auto', povm_type='auto', instrument_type='auto', ideal_model=None, cptp_truncation_tol=1e-06)

Convert all gates, states, and POVMs to a specific parameterization type.

Parameters

parameterization_typestring

The gate, state, and POVM parameterization type. Allowed values are (where ‘*’ means “ terms” and “ clifford terms” evolution-type suffixes are allowed):

• “full” : each gate / state / POVM effect element is an independent parameter

• “TP” : Trace-Preserving gates and state preps

• “static” : no parameters

• “static unitary” : no parameters; convert superops to unitaries

• “clifford” : no parameters; convert unitaries to Clifford symplecitics.

• “GLND*” : General unconstrained Lindbladian

• “CPTP*” : Completely-Positive-Trace-Preserving

• “H+S+A*” : Hamiltoian, Pauli-Stochastic, and Affine errors

• “H+S*” : Hamiltonian and Pauli-Stochastic errors

• “S+A*” : Pauli-Stochastic and Affine errors

• “S*” : Pauli-Stochastic errors

• “H+D+A*” : Hamiltoian, Depolarization, and Affine errors

• “H+D*” : Hamiltonian and Depolarization errors

• “D+A*” : Depolarization and Affine errors

• “D*” : Depolarization errors

• Any of the above with “S” replaced with “s” or “D” replaced with “d”. This removes the CPTP constraint on the gates and SPAM operations (and as such is seldom used).

ideal_modelModel, optional

This may specify an ideal model of unitary gates and pure state vectors to be used as the ideal operation of each gate/SPAM operation, which is particularly useful as target for CPTP-based conversions.

cptp_truncation_tolfloat, optional (default 1e-6)

Tolerance used for conversion to CPTP parameterizations. When converting to CPTP models negative eigenvalues of the choi matrix representation of a superoperator are truncated, which can result in a change in the PTM for that operator. This tolerance indicates the maximum amount of truncation induced deviation from the original operations (measured by frobenius distance) we’re willing to accept without marking the conversion as failed.

Returns

None

deriv_wrt_params()

The element-wise derivative of all this models’ operations.

Constructs a matrix whose columns are the vectorized derivatives of all the model’s raw matrix and vector elements (placed in a vector) with respect to each single model parameter.

Thus, each column has length equal to the number of elements in the model, and there are num_params() columns. In the case of a “fully parameterized model” (i.e. all operation matrices and SPAM vectors are fully parameterized) then the resulting matrix will be the (square) identity matrix.

Returns

numpy array

2D array of derivatives.

compute_nongauge_and_gauge_spaces(item_weights=None, non_gauge_mix_mx=None)

TODO: docstring

compute_nongauge_projector(item_weights=None, non_gauge_mix_mx=None)

Construct a projector onto the non-gauge parameter space.

Useful for isolating the gauge degrees of freedom from the non-gauge degrees of freedom.

Parameters

item_weightsdict, optional

Dictionary of weighting factors for individual gates and spam operators. Keys can be gate, state preparation, POVM effect, spam labels, or the special strings “gates” or “spam” whic represent the entire set of gate or SPAM operators, respectively. Values are floating point numbers. These weights define the metric used to compute the non-gauge space, orthogonal the gauge space, that is projected onto.

non_gauge_mix_mxnumpy array, optional

An array of shape (n_non_gauge_params,n_gauge_params) specifying how to mix the non-gauge degrees of freedom into the gauge degrees of freedom that are projected out by the returned object. This argument essentially sets the off-diagonal block of the metric used for orthogonality in the “gauge + non-gauge” space. It is for advanced usage and typically left as None (the default).

Returns

numpy array

The projection operator as a N x N matrix, where N is the number of parameters (obtained via num_params()). This projector acts on parameter-space, and has rank equal to the number of non-gauge degrees of freedom.

transform_inplace(s)

Gauge transform this model.

Update each of the operation matrices G in this model with inv(s) * G * s, each rhoVec with inv(s) * rhoVec, and each EVec with EVec * s

Parameters

sGaugeGroupElement

A gauge group element which specifies the “s” matrix (and it’s inverse) used in the above similarity transform.

Returns

None

frobeniusdist(other_model, transform_mx=None, item_weights=None, normalize=True)

Compute the weighted frobenius norm of the difference between this model and other_model.

Differences in each corresponding gate matrix and spam vector element are squared, weighted (using item_weights as applicable), then summed. The value returned is the square root of this sum, or the square root of this sum divided by the number of summands if normalize == True.

Parameters

other_modelModel

the other model to difference against.

transform_mxnumpy array, optional

if not None, transform this model by G => inv(transform_mx) * G * transform_mx, for each operation matrix G (and similar for rho and E vectors) before taking the difference. This transformation is applied only for the difference and does not alter the values stored in this model.

item_weightsdict, optional

Dictionary of weighting factors for individual gates and spam operators. Weights are applied multiplicatively to the squared differences, i.e., (before the final square root is taken). Keys can be gate, state preparation, POVM effect, or spam labels, as well as the two special labels “gates” and “spam” which apply to all of the gate or SPAM elements, respectively (but are overridden by specific element values). Values are floating point numbers. By default, all weights are 1.0.

normalizebool, optional

if True (the default), the sum of weighted squared-differences is divided by the weighted number of differences before the final square root is taken. If False, the division is not performed.

Returns

float

residuals(other_model, transform_mx=None, item_weights=None)

Compute the weighted residuals between two models.

Residuals are the differences in corresponding operation matrix and spam vector elements.

Parameters

other_modelModel

the other model to difference against.

transform_mxnumpy array, optional

if not None, transform this model by G => inv(transform_mx) * G * transform_mx, for each operation matrix G (and similar for rho and E vectors) before taking the difference. This transformation is applied only for the difference and does not alter the values stored in this model.

item_weightsdict, optional

Dictionary of weighting factors for individual gates and spam operators. Weights applied such that they act multiplicatively on the squared differences, so that the residuals themselves are scaled by the square roots of these weights. Keys can be gate, state preparation, POVM effect, or spam labels, as well as the two special labels “gates” and “spam” which apply to all of the gate or SPAM elements, respectively (but are overridden by specific element values). Values are floating point numbers. By default, all weights are 1.0.

Returns

residualsnumpy.ndarray

A 1D array of residuals (differences w.r.t. other)

nSummandsint

The (weighted) number of elements accounted for by the residuals.

jtracedist(other_model, transform_mx=None, include_spam=True)

Compute the Jamiolkowski trace distance between this model and other_model.

This is defined as the maximum of the trace distances between each corresponding gate, including spam gates.

Parameters

other_modelModel

the other model to difference against.

transform_mxnumpy array, optional

if not None, transform this model by G => inv(transform_mx) * G * transform_mx, for each operation matrix G (and similar for rho and E vectors) before taking the difference. This transformation is applied only for the difference and does not alter the values stored in this model.

include_spambool, optional

Whether to add to the max-trace-distance the frobenius distances between corresponding SPAM operations.

Returns

float

diamonddist(other_model, transform_mx=None, include_spam=True)

Compute the diamond-norm distance between this model and other_model.

This is defined as the maximum of the diamond-norm distances between each corresponding gate, including spam gates.

Parameters

other_modelModel

the other model to difference against.

transform_mxnumpy array, optional

if not None, transform this model by G => inv(transform_mx) * G * transform_mx, for each operation matrix G (and similar for rho and E vectors) before taking the difference. This transformation is applied only for the difference and does not alter the values stored in this model.

include_spambool, optional

Whether to add to the max-diamond-distance the frobenius distances between corresponding SPAM operations.

Returns

float

strdiff(other_model, metric='frobenius')

Return a string describing the distances between this model and other_model.

The returned string displays differences between each corresponding gate, state prep, and POVM effect.

Parameters

other_modelModel

the other model to difference against.

metric{‘frobenius’, ‘infidelity’, ‘diamond’}

Which distance metric to use.

Returns

str

all_objects()

Iterate over all of the (label, operator object) entities in this model.

This iterator runs over all state preparations, POVMS, operations, and instruments.

depolarize(op_noise=None, spam_noise=None, max_op_noise=None, max_spam_noise=None, seed=None)

Apply depolarization uniformly or randomly to this model’s gate and/or SPAM elements.

The result is returned without modifying the original (this) model. You must specify either op_noise or max_op_noise (for the amount of gate depolarization), and either spam_noise or max_spam_noise (for spam depolarization).

Parameters

op_noisefloat, optional

apply depolarizing noise of strength 1-op_noise to all gates in

the model. (Multiplies each assumed-Pauli-basis operation matrix by the diagonal matrix with (1.0-op_noise) along all the diagonal elements except the first (the identity).

spam_noisefloat, optional

apply depolarizing noise of strength 1-spam_noise to all SPAM opeations (state and POVM effects) in the model. (Multiplies the non-identity part of each assumed-Pauli-basis state preparation vector and measurement vector by (1.0-spam_noise)).

max_op_noisefloat, optional

specified instead of op_noise; apply a random depolarization with maximum strength 1-max_op_noise to each gate in the model.

max_spam_noisefloat, optional

specified instead of spam_noise; apply a random depolarization with maximum strength 1-max_spam_noise to each state preparation and POVM in the model.

seedint, optional

if not None, seed numpy’s random number generator with this value before generating random depolarizations.

Returns

Model

the depolarized Model

rotate(rotate=None, max_rotate=None, seed=None)

Apply a rotation uniformly or randomly to this model.

Uniformly means the same rotation applied to each gate and randomly means different random rotations are applied to each gate of this model. The result is returned without modifying the original (this) model.

You must specify either rotate or max_rotate. This method currently only works on n-qubit models.

Parameters

rotatetuple of floats, optional

If you specify the rotate argument, then the same rotation operation is applied to each gate. That is, each gate’s matrix G is composed with a rotation operation R (so G -> dot(R, G) ) where R is the unitary superoperator corresponding to the unitary operator U = exp( sum_k( i * rotate[k] / 2.0 * Pauli_k ) ). Here Pauli_k ranges over all of the non-identity un-normalized Pauli operators (e.g. {X,Y,Z} for 1 qubit, {IX, IY, IZ, XI, XX, XY, XZ, YI, YX, YY, YZ, ZI, ZX, ZY, ZZ} for 2 qubits).

max_rotatefloat, optional

If max_rotate is specified (instead of rotate), then pyGSTi randomly generates a different rotate tuple, and applies the corresponding rotation, to each gate in this Model. Each component of each tuple is drawn uniformly from [0, max_rotate).

seedint, optional

if not None, seed numpy’s random number generator with this value before generating random depolarizations.

Returns

Model

the rotated Model

randomize_with_unitary(scale, seed=None, rand_state=None)

Create a new model with random unitary perturbations.

Apply a random unitary to each element of a model, and return the result, without modifying the original (this) model. This method works on Model as long as the dimension is a perfect square.

Parameters

scalefloat

maximum element magnitude in the generator of each random unitary transform.

seedint, optional

if not None, seed numpy’s random number generator with this value before generating random depolarizations.

rand_statenumpy.random.RandomState

A RandomState object to generate samples from. Can be useful to set instead of seed if you want reproducible distribution samples across multiple random function calls but you don’t want to bother with manually incrementing seeds between those calls.

Returns

Model

the randomized Model

increase_dimension(new_dimension)

Enlarge the dimension of this model.

Enlarge the spam vectors and operation matrices of model to a specified dimension, and return the resulting inflated model. Spam vectors are zero-padded and operation matrices are padded with 1’s on the diagonal and zeros on the off-diagonal (effectively padded by identity operation).

Parameters

new_dimensionint

the dimension of the returned model. That is, the returned model will have rho and E vectors that have shape (new_dimension,1) and operation matrices with shape (new_dimension,new_dimension)

Returns

Model

the increased-dimension Model

kick(absmag=1.0, bias=0, seed=None)

“Kick” this model by adding to each gate a random matrix.

The random matrices have values uniformly distributed in the interval [bias-absmag,bias+absmag].

Parameters

absmagfloat, optional

The maximum magnitude of the entries in the “kick” matrix relative to bias.

biasfloat, optional

The bias of the entries in the “kick” matrix.

seedint, optional

if not None, seed numpy’s random number generator with this value before generating random depolarizations.

Returns

Model

the kicked model.

compute_clifford_symplectic_reps(oplabel_filter=None)

Constructs a dictionary of the symplectic representations for all the Clifford gates in this model.

Non-StaticCliffordOp gates will be ignored and their entries omitted from the returned dictionary.

Parameters

oplabel_filteriterable, optional

A list, tuple, or set of operation labels whose symplectic representations should be returned (if they exist).

Returns

dict

keys are operation labels and/or just the root names of gates (without any state space indices/labels). Values are (symplectic_matrix, phase_vector) tuples.

print_info()

Print to stdout relevant information about this model.

This information includes the Choi matrices and their eigenvalues.

Returns

None

create_processor_spec(qudit_labels='auto')

Create a processor specification from this model with the given qudit labels.

Currently this only works for models on qudits.

Parameters

qudit_labelstuple or “auto”, optional

A tuple of qudit labels, e.g. (‘Q0’, ‘Q1’) or (0, 1). “auto” uses the labels in this model’s state space labels.

Returns

QuditProcessorSpec or QubitProcessorSpec

create_modelmember_graph()

Generate a ModelMemberGraph for the model.

Returns

ModelMemberGraph

A directed graph capturing dependencies among model members

errorgen_coefficients(normalized_elem_gens=True)

TODO: docstring - returns a nested dict containing all the error generator coefficients for all the operations in this model.

class pygsti.models.explicitmodel.ExplicitLayerRules

Bases: pygsti.models.layerrules.LayerRules

Rule: layer must appear explicitly as a “primitive op”

prep_layer_operator(model, layerlbl, caches)

Create the operator corresponding to layerlbl.

Parameters

layerlblLabel

A circuit layer label.

Returns

State

povm_layer_operator(model, layerlbl, caches)

Create the operator corresponding to layerlbl.

Parameters

layerlblLabel

A circuit layer label.

Returns

POVM or POVMEffect

operation_layer_operator(model, layerlbl, caches)

Create the operator corresponding to layerlbl.

Parameters

layerlblLabel

A circuit layer label.

Returns

LinearOperator