# Release notes¶

## Release 0.6.0 (development release)¶

### New features¶

### Breaking changes¶

### Improvements¶

### Bug fixes¶

Fixed a bug about the variable names in functions (apply_kraus_to_ket, apply_kraus_to_dm, apply_choi_to_ket, apply_choi_to_dm). (#271)

### Documentation¶

### Contributors¶

## Release 0.5.0 (current release)¶

### New features¶

Optimization callback functionalities has been improved. A dedicated

`Callback`

class is added which is able to access the optimizer, the cost function, the parameters as well as gradients, during the optimization. In addition, multiple callbacks can be specified. This opens up the endless possiblities of customizing the the optimization progress with schedulers, trackers, heuristics, tricks, etc. (#219)Tensorboard-based optimization tracking is added as a builtin

`Callback`

class:`TensorboardCallback`

. It can automatically track costs as well as all trainable parameters during optimization in realtime. Tensorboard can be most conveniently viewed from VScode. (#219)import numpy as np from mrmustard.training import Optimizer, TensorboardCallback def cost_fn(): ... def as_dB(cost): delta = np.sqrt(np.log(1 / (abs(cost) ** 2)) / (2 * np.pi)) cost_dB = -10 * np.log10(delta**2) return cost_dB tb_cb = TensorboardCallback(cost_converter=as_dB, track_grads=True) opt = Optimizer(euclidean_lr = 0.001); opt.minimize(cost_fn, max_steps=200, by_optimizing=[...], callbacks=tb_cb) # Logs will be stored in `tb_cb.logdir` which defaults to `./tb_logdir/...` but can be customized. # VScode can be used to open the Tensorboard frontend for live monitoring. # Or, in command line: `tensorboard --logdir={tb_cb.logdir}` and open link in browser.

Gaussian states support a

`bargmann`

method for returning the bargmann representation. (#235)The

`ket`

method of`State`

now supports new keyword arguments`max_prob`

and`max_photons`

. Use them to speed-up the filling of a ket array up to a certain probability or*total*photon number. (#235)from mrmustard.lab import Gaussian # Fills the ket array up to 99% probability or up to the |0,3>, |1,2>, |2,1>, |3,0> subspace, whichever is reached first. # The array has the autocutoff shape, unless the cutoffs are specified explicitly. ket = Gaussian(2).ket(max_prob=0.99, max_photons=3)

Gaussian transformations support a

`bargmann`

method for returning the bargmann representation. (#239)BSGate.U now supports method=’vanilla’ (default) and ‘schwinger’ (slower, but stable to any cutoff) (#248)

### Breaking Changes¶

### Improvements¶

The math module now has a submodule

`lattice`

for constructing recurrence relation strategies in the Fock lattice. There are a few predefined strategies in`mrmustard.math.lattice.strategies`

. (#235)Gradients in the Fock lattice are now computed using the vector-jacobian product. This saves a lot of memory and speeds up the optimization process by roughly 4x. (#235)

Tests of the compact_fock module now use hypothesis. (#235)

Faster implementation of the fock representation of

`BSgate`

,`Sgate`

and`SqueezedVacuum`

, ranging from 5x to 50x. (#239)More robust implementation of cutoffs for States. (#239)

Dependencies and versioning are now managed using Poetry. (#257)

### Bug fixes¶

Fixed a bug that would make two progress bars appear during an optimization (#235)

The displacement of the dual of an operation had the wrong sign (#239)

When projecting a Gaussian state onto a Fock state, the upper limit of the autocutoff now respect the Fock projection. (#246)

Fixed a bug for the algorithms that allow faster PNR sampling from Gaussian circuits using density matrices. When the cutoff of the first detector is equal to 1, the resulting density matrix is now correct.

### Documentation¶

### Contributors¶

Filippo Miatto, Zeyue Niu, Robbe De Prins, Gabriele Gullì, Richard A. Wolf

## Release 0.4.1¶

### New features¶

### Breaking changes¶

### Improvements¶

### Bug fixes¶

### Documentation¶

### Contributors¶

## Release 0.4.0 (current release)¶

### New features¶

Ray-based distributed trainer is now added to

`training.trainer`

. It acts as a replacement for`for`

loops and enables the parallelization of running many circuits as well as their optimizations. To install the extra dependencies:`pip install .[ray]`

. (#194)from mrmustard.lab import Vacuum, Dgate, Ggate from mrmustard.physics import fidelity from mrmustard.training.trainer import map_trainer def make_circ(x=0.): return Ggate(num_modes=1, symplectic_trainable=True) >> Dgate(x=x, x_trainable=True, y_trainable=True) def cost_fn(circ=make_circ(0.1), y_targ=0.): target = Gaussian(1) >> Dgate(-1.5, y_targ) s = Vacuum(1) >> circ return -fidelity(s, target) # Use case 0: Calculate the cost of a randomly initialized circuit 5 times without optimizing it. results_0 = map_trainer( cost_fn=cost_fn, tasks=5, ) # Use case 1: Run circuit optimization 5 times on randomly initialized circuits. results_1 = map_trainer( cost_fn=cost_fn, device_factory=make_circ, tasks=5, max_steps=50, symplectic_lr=0.05, ) # Use case 2: Run circuit optimization 2 times on randomly initialized circuits with custom parameters. results_2 = map_trainer( cost_fn=cost_fn, device_factory=make_circ, tasks=[ {'x': 0.1, 'euclidean_lr': 0.005, 'max_steps': 50, 'HBAR': 1.}, {'x': -0.7, 'euclidean_lr': 0.1, 'max_steps': 2, 'HBAR': 2.}, ], y_targ=0.35, symplectic_lr=0.05, AUTOCUTOFF_MAX_CUTOFF=7, )

Sampling for homodyne measurements is now integrated in Mr Mustard: when no measurement outcome value is specified by the user, a value is sampled from the reduced state probability distribution and the conditional state on the remaining modes is generated. (#143)

import numpy as np from mrmustard.lab import Homodyne, TMSV, SqueezedVacuum # conditional state from measurement conditional_state = TMSV(r=0.5, phi=np.pi)[0, 1] >> Homodyne(quadrature_angle=np.pi/2)[1] # measurement outcome measurement_outcome = SqueezedVacuum(r=0.5) >> Homodyne()

The optimizer

`minimize`

method now accepts an optional callback function, which will be called at each step of the optimization and it will be passed the step number, the cost value, and the value of the trainable parameters. The result is added to the`callback_history`

attribute of the optimizer. (#175)the Math interface now supports linear system solving via

`math.solve`

. (#185)We introduce the tensor wrapper

`MMTensor`

(available in`math.mmtensor`

) that allows for a very easy handling of tensor contractions. Internally MrMustard performs lots of tensor contractions and this wrapper allows one to label each index of a tensor and perform contractions using the`@`

symbol as if it were a simple matrix multiplication (the indices with the same name get contracted). (#185)

(#195)from mrmustard.math.mmtensor import MMTensor # define two tensors A = MMTensor(np.random.rand(2, 3, 4), axis_labels=["foo", "bar", "contract"]) B = MMTensor(np.random.rand(4, 5, 6), axis_labels=["contract", "baz", "qux"]) # perform a tensor contraction C = A @ B C.axis_labels # ["foo", "bar", "baz", "qux"] C.shape # (2, 3, 5, 6) C.tensor # extract actual result

MrMustard’s settings object (accessible via

`from mrmustard import settings`

) now supports`SEED`

(an int). This will give reproducible results whenever randomness is involved. The seed is assigned randomly by default, and it can be reassigned again by setting it to None:`settings.SEED = None`

. If one desires, the seeded random number generator is accessible directly via`settings.rng`

(e.g.`settings.rng.normal()`

). (#183)The

`Circuit`

class now has an ascii representation, which can be accessed via the repr method. It looks great in Jupyter notebooks! There is a new option at`settings.CIRCUIT_DECIMALS`

which controls the number of decimals shown in the ascii representation of the gate parameters. If`None`

, only the name of the gate is shown. (#196)PNR sampling from Gaussian circuits using density matrices can now be performed faster. When all modes are detected, this is done by replacing

`math.hermite_renormalized`

by`math.hermite_renormalized_diagonal`

. If all but the first mode are detected,`math.hermite_renormalized_1leftoverMode`

can be used. The complexity of these new methods is equal to performing a pure state simulation. The methods are differentiable, so that they can be used for defining a cost function. (#154)MrMustard repo now provides a fully furnished vscode development container and a Dockerfile. To find out how to use dev containers for development check the documentation here. (#214)

### Breaking changes¶

### Improvements¶

The

`Dgate`

is now implemented directly in MrMustard (instead of on The Walrus) to calculate the unitary and gradients of the displacement gate in Fock representation, providing better numerical stability for larger cutoff and displacement values. (#147) (#211)Now the Wigner function is implemented in its own module and uses numba for speed. (#171)

from mrmustard.utils.wigner import wigner_discretized W, Q, P = wigner_discretized(dm, q, p) # dm is a density matrix

Calculate marginals independently from the Wigner function thus ensuring that the marginals are physical even though the Wigner function might not contain all the features of the state within the defined window. Also, expose some plot parameters and return the figure and axes. (#179)

Allows for full cutoff specification (index-wise rather than mode-wise) for subclasses of

`Transformation`

. This allows for a more compact Fock representation where needed. (#181)The

`mrmustard.physics.fock`

module now provides convenience functions for applying kraus operators and choi operators to kets and density matrices. (#180)from mrmustard.physics.fock import apply_kraus_to_ket, apply_kraus_to_dm, apply_choi_to_ket, apply_choi_to_dm ket_out = apply_kraus_to_ket(kraus, ket_in, indices) dm_out = apply_choi_to_dm(choi, dm_in, indices) dm_out = apply_kraus_to_dm(kraus, dm_in, indices) dm_out = apply_choi_to_ket(choi, ket_in, indices)

Replaced norm with probability in the repr of

`State`

. This improves consistency over the old behaviour (norm was the sqrt of prob if the state was pure and prob if the state was mixed). (#182)Added two new modules (

`physics.bargmann`

and`physics.husimi`

) to host the functions related to those representations, which have been refactored and moved out of`physics.fock`

. (#185)The internal type system in MrMustard has been beefed up with much clearer types, like ComplexVector, RealMatrix, etc… as well as a generic type

`Batch`

, which can be parametrized using the other types, like`Batch[ComplexTensor]`

. This will allow for better type checking and better error messages. (#199)Added multiple tests and improved the use of Hypothesis. (#191)

The

`fock.autocutoff`

function now uses the new diagonal methods for calculating a probability-based cutoff. Use`settings.AUTOCUTOFF_PROBABILITY`

to set the probability threshold. (#203)The unitary group optimization (for the interferometer) and the orthogonal group optimization (for the real interferometer) have been added. The symplectic matrix that describes an interferometer belongs to the intersection of the orthogonal group and the symplectic group, which is a unitary group, so we needed both. (#208)

### Bug fixes¶

The

`Dgate`

and the`Rgate`

now correctly parse the case when a single scalar is intended as the same parameter of a number of gates in parallel. (#180)The trace function in the fock module was giving incorrect results when called with certain choices of modes. This is now fixed. (#180)

The purity function for fock states no longer normalizes the density matrix before computing the purity. (#180)

The function

`dm_to_ket`

no longer normalizes the density matrix before diagonalizing it. (#180)The internal fock representation of states returns the correct cutoffs in all cases (solves an issue when a pure dm was converted to ket). (#184)

The ray related tests were hanging in github action causing tests to halt and fail. Now ray is forced to init with 1 cpu when running tests preventing the issue. (#201)

Various minor bug fixes. (#202)

Fixed the issue that the optimization of the interferometer was using orthogonal group optimization rather than unitary. (#208)

Fixes a slicing issue that arises when we compute the fidelity between gaussian and fock states. (#210)

The sign of parameters in the circuit drawer are now displayed correctly. (#209)

Fixed a bug in the Gaussian state which caused its covariance matrix to be multiplied by hbar/2 twice. Adds the argument

`modes`

to`Ggate`

. (#212)Fixes a bug in the cutoffs of the choi operator. (#216)

### Documentation¶

### Contributors¶

This release contains contributions from (in alphabetical order): Robbe De Prins, Sebastian Duque Mesa, Filippo Miatto, Zeyue Niu, Yuan Yao

## Release 0.3.0¶

### New features¶

Can switch progress bar on and off (default is on) from the settings via

`settings.PROGRESSBAR = True/False`

. (#128)States in Gaussian and Fock representation now can be concatenated.

from mrmustard.lab.states import Gaussian, Fock from mrmustard.lab.gates import Attenuator # concatenate pure states fock_state = Fock(4) gaussian_state = Gaussian(1) pure_state = fock_state & gaussian_state # also can concatenate mixed states mixed1 = fock_state >> Attenuator(0.8) mixed2 = gaussian_state >> Attenuator(0.5) mixed_state = mixed1 & mixed2 mixed_state.dm()

Parameter passthrough allows one to use custom variables and/or functions as parameters. For example we can use parameters of other gates:

from mrmustard.lab.gates import Sgate, BSgate BS = BSgate(theta=np.pi/4, theta_trainable=True)[0,1] S0 = Sgate(r=BS.theta)[0] S1 = Sgate(r=-BS.theta)[1] circ = S0 >> S1 >> BS

Another possibility is with functions:

def my_r(x): return x**2 x = math.new_variable(0.5, bounds = (None, None), name="x") def cost_fn(): # note that my_r needs to be in the cost function # in order to track the gradient S = Sgate(r=my_r(x), theta_trainable=True)[0,1] return # some function of S opt.Optimize(cost_fn, by_optimizing=[x])

Adds the new trainable gate

`RealInterferometer`

: an interferometer that doesn’t mix the q and p quadratures. (#132)Now marginals can be iterated over:

for mode in state: print(mode.purity)

### Breaking changes¶

The Parametrized and Training classes have been refactored: now trainable tensors are wrapped in an instance of the

`Parameter`

class. To define a set of parameters dofrom mrmustard.training import Parametrized params = Parametrized( magnitude=10, magnitude_trainable=False, magnitude_bounds=None, angle=0.1, angle_trainable=True, angle_bounds=(-0.1,0.1) )

which will automatically define the properties

`magnitude`

and`angle`

on the`params`

object. To access the backend tensor defining the values of such parameters use the`value`

propertyparams.angle.value params.angle.bounds params.magnitude.value

Gates will automatically be an instance of the

`Parametrized`

class, for examplefrom mrmustard.lab import BSgate bs = BSgate(theta = 0.3, phi = 0.0, theta_trainable: True) # access params bs.theta.value bs.theta.bounds bs.phi.value

### Improvements¶

The Parametrized and Training classes have been refactored. The new training module has been added and with it the new

`Parameter`

class: now trainable tensors are being wrapped in an instance of`Parameter`

. (#133), patch (#144)The string representations of the

`Circuit`

and`Transformation`

objects have been improved: the`Circuit.__repr__`

method now produces a string that can be used to generate a circuit in an identical state (same gates and parameters), the`Transformation.__str__`

and objects inheriting from it now prints the name, memory location of the object as well as the modes of the circuit in which the transformation is acting on. The`_markdown_repr_`

has been implemented and on a jupyter notebook produces a table with valuable information of the Transformation objects. (#141)Add the argument ‘modes’ to the

`Interferometer`

operation to indicate which modes the Interferometer is applied to. (#121)

### Bug fixes¶

Fixed a bug in the

`State.ket()`

method. An attribute was called with a typo in its name. (#135)The

`math.dagger`

function applying the hermitian conjugate to an operator was incorrectly transposing the indices of the input tensor. Now`math.dagger`

appropriately calculates the Hermitian conjugate of an operator. (#156)The application of a Choi operator to a density matrix was resulting in a transposed dm. Now the order of the indices in the application of a choi operator to dm and ket is correct. (#188)

### Documentation¶

The centralized Xanadu Sphinx Theme is now used to style the Sphinx documentation. (#126)

The documentation now contains the

`mm.training`

section. The optimization examples on the README and Basic API Reference section have been updated to use the latest API. (#133)

### Contributors¶

This release contains contributions from (in alphabetical order):

Mikhail Andrenkov, Sebastian Duque Mesa, Filippo Miatto, Yuan Yao

## Release 0.2.0¶

### New features since last release¶

### Improvements¶

The tensorflow and torch backend adhere to

`MathInterface`

. (#103)

### Bug fixes¶

### Documentation¶

Basic API reference is updated to use the latest Mr Mustard API. (#119)

### Contributors¶

This release contains contributions from (in alphabetical order):

## Release 0.1.1¶

### New features since last release¶

### Improvements since last release¶

### Bug fixes¶

### Contributors¶

This release contains contributions from (in alphabetical order):

## Release 0.1.0¶

### New features since last release¶

This is the initial public release.

### Contributors¶

This release contains contributions from (in alphabetical order):

Sebastián Duque, Zhi Han, Theodor Isacsson, Josh Izaac, Filippo Miatto, Nicolas Quesada