Release 0.37.0

New features since last release

Execute wide circuits with Default Tensor 🔗

A new default.tensor device is now available for performing tensor network and matrix product state simulations of quantum circuits using the quimb backend. (#5699) (#5744) (#5786) (#5795)

Either method can be selected when instantiating the default.tensor device by setting the method keyword argument to "tn" (tensor network) or "mps" (matrix product state).

There are several templates in PennyLane that are tensor-network focused, which are excellent candidates for the "tn" method for default.tensor. The following example shows how a circuit comprising gates in a tree tensor network architecture can be efficiently simulated using method="tn".

import pennylane as qml

n_wires = 16
dev = qml.device("default.tensor", method="tn")

def block(weights, wires):
    qml.CNOT(wires=[wires[0], wires[1]])
    qml.RY(weights[0], wires=wires[0])
    qml.RY(weights[1], wires=wires[1])

n_block_wires = 2
n_params_block = 2
n_blocks = qml.TTN.get_n_blocks(range(n_wires), n_block_wires)
template_weights = [[0.1, -0.3]] * n_blocks

@qml.qnode(dev)
def circuit(template_weights):
    for i in range(n_wires):
        qml.Hadamard(i)
    qml.TTN(range(n_wires), n_block_wires, block, n_params_block, template_weights)
    return qml.expval(qml.Z(n_wires - 1))

>>> circuit(template_weights)
0.3839174759751649

For matrix product state simulations (method="mps"), we can make the execution be approximate by setting max_bond_dim (see the device's documentation for more details). The maximum bond dimension has implications for the speed of the simulation and lets us control the degree of the approximation, as shown in the following example. First, set up the circuit:

import numpy as np

n_layers = 10 
n_wires = 10
initial_shape, weights_shape = qml.SimplifiedTwoDesign.shape(n_layers, n_wires) 
np.random.seed(1967) 
initial_layer_weights = np.random.random(initial_shape) 
weights = np.random.random(weights_shape)

def f(): 
    qml.SimplifiedTwoDesign(initial_layer_weights, weights, range(n_wires)) 
    return qml.expval(qml.Z(0))

The default.tensor device is instantiated with a max_bond_dim value:

dev_dq = qml.device("default.qubit") 
value_dq = qml.QNode(f, dev_dq)()

dev_mps = qml.device("default.tensor", max_bond_dim=5) 
value_mps = qml.QNode(f, dev_mps)()

With this bond dimension, the expectation values calculated for default.qubit and default.tensor are different:

>>> np.abs(value_dq - value_mps) 
tensor(0.0253213, requires_grad=True)

Learn more about default.tensor and how to configure it by visiting the how-to guide.

Add noise models to your quantum circuits 📺

Support for building noise models and applying them to a quantum circuit has been added via the NoiseModel class and an add_noise transform. (#5674) (#5684) (#5718)

Under the hood, PennyLane's approach to noise models is insertion-based, meaning that noise is included by inserting additional operators (gates or channels) that describe the noise into the quantum circuit. Creating a NoiseModel boils down to defining Boolean conditions under which specific noisy operations are inserted. There are several ways to specify conditions for adding noisy operations:
- qml.noise.op_eq(op): if the operator op is encountered in the circuit, add noise.
- qml.noise.op_in(ops): if any operators in ops are encountered in the circuit, add noise.
- qml.noise.wires_eq(wires): if an operator is applied to wires, add noise.
- qml.noise.wires_in(wires): if an operator is applied to any wire in wires, add noise.
- custom noise conditions: custom conditions can be defined as functions decorated with qml.BooleanFn that return a Boolean value. For example, the following function will insert noise if a qml.RY operator is encountered with an angle of rotation that is less than 0.5:
```
@qml.BooleanFn 
def c0(op): 
    return isinstance(op, qml.RY) and op.parameters[0] < 0.5 
```
Conditions can also be combined together with &, and, |, etc. Once the conditions under which noise is to be inserted have been stated, we can specify exactly what noise is inserted with the following:
- qml.noise.partial_wires(op): insert op on the wires that are specified by the condition that triggers adding this noise
- custom noise operations: custom noise can be specified by defining a standard quantum function like below.
```
def n0(op, **kwargs): 
    qml.RY(op.parameters[0] * 0.05, wires=op.wires) 
```
With that, we can create a qml.NoiseModel object whose argument must be a dictionary mapping conditions to noise:
```
c1 = qml.noise.op_eq(qml.X) & qml.noise.wires_in([0, 1]) 
n1 = qml.noise.partial_wires(qml.AmplitudeDamping, 0.4)

noise_model = qml.NoiseModel({c0: n0, c1: n1}) 
```
```
>>> noise_model 
NoiseModel({ BooleanFn(c0): n0 OpEq(PauliX) | WiresIn([0, 1]): AmplitudeDamping(gamma=0.4) }) 
```
The noise model created can then be added to a QNode with qml.add_noise:
```
dev = qml.device("lightning.qubit", wires=3)

@qml.qnode(dev) 
def circuit(): 
    qml.Y(0) 
    qml.CNOT([0, 1]) 
    qml.RY(0.3, wires=2) # triggers c0 
    qml.X(1) # triggers c1 
    return qml.state() 
```
```
>>> print(qml.draw(circuit)()) 
0: ──Y────────╭●────┤ State 
1: ───────────╰X──X─┤ State 
2: ──RY(0.30)───────┤ State 
>>> circuit = qml.add_noise(circuit, noise_model) 
>>> print(qml.draw(circuit)()) 
0: ──Y────────╭●───────────────────────────────────┤ State 
1: ───────────╰X─────────X──AmplitudeDamping(0.40)─┤ State 
2: ──RY(0.30)──RY(0.01)────────────────────────────┤ State 
```
If more than one transform is applied to a QNode, control over when/where the add_noise transform is applied in relation to the other transforms can be specified with the level keyword argument. By default, add_noise is applied after all the transforms that have been manually applied to the QNode until that point. To learn more about this new functionality, check out our noise module documentation and keep your eyes peeled for an in-depth demo!

Catch bugs with the PennyLane debugger 🚫🐞

The new PennyLane quantum debugger allows pausing simulation via the qml.breakpoint() command and provides tools for analyzing quantum circuits during execution. (#5680) (#5749) (#5789)

This includes monitoring the circuit via measurements using qml.debug_state(), qml.debug_probs(), qml.debug_expval(), and qml.debug_tape(), stepping through the operations in a quantum circuit, and interactively adding operations during execution.

Including qml.breakpoint() in a circuit will cause the simulation to pause during execution and bring up the interactive console. For example, consider the following code in a Python file called script.py:
```
@qml.qnode(qml.device('default.qubit', wires=(0,1,2))) 
def circuit(x): 
    qml.Hadamard(wires=0) 
    qml.CNOT(wires=(0,2)) 
    qml.breakpoint()

    qml.RX(x, wires=1) 
    qml.RY(x, wires=2) 
    qml.breakpoint()

    return qml.sample()

circuit(1.2345) 
```
Upon executing script.py, the simulation pauses at the first breakpoint:
```
> /Users/your/path/to/script.py(8)circuit()
-> qml.RX(x, wires=1) 
[pldb] 
```
While debugging, we can access circuit information. For example, qml.debug_tape() returns the tape of the circuit, giving access to its operations and drawing:
```
[pldb] tape = qml.debug_tape() 
[pldb] print(tape.draw(wire_order=[0,1,2])) 
0: ──H─╭●─┤ 
2: ────╰X─┤ 
[pldb] tape.operations 
[Hadamard(wires=[0]), CNOT(wires=[0, 2])] 
```
While qml.debug_state() is equivalent to qml.state() and gives the current state:
```
[pldb] print(qml.debug_state()) 
[0.70710678+0.j 0. +0.j 0. +0.j 0. +0.j 1. +0.j 0.70710678+0.j 0. +0.j 0. +0.j] 
```
Other debugger functions like qml.debug_probs() and qml.debug_expval() also function like their simulation counterparts (qml.probs and qml.expval, respectively) and are described in more detail in the debugger documentation Additionally, standard debugging commands are available to navigate through code, including list, longlist, next, continue, and quit, as described in the debugging documentation. Finally, to modify a circuit mid-run, simply call the desired PennyLane operations:
```
[pldb] qml.CNOT(wires=(0,2)) 
CNOT(wires=[0, 2]) 
[pldb] print(qml.debug_tape().draw(wire_order=[0,1,2])) 
0: ──H─╭●─╭●─┤ 
2: ────╰X─╰X─┤ 
```

Stay tuned for an in-depth demonstration on using this feature with real-world examples!

Convert between OpenFermion and PennyLane 🤝

Two new functions called qml.from_openfermion and qml.to_openfermion are now available to convert between OpenFermion and PennyLane objects. This includes both fermionic and qubit operators. (#5773) (#5808) (#5881)

For fermionic operators:

>>> import openfermion 
>>> of_fermionic = openfermion.FermionOperator('0^ 2') 
>>> type(of_fermionic) 
<class 'openfermion.ops.operators.fermion_operator.FermionOperator'> 
>>> pl_fermionic = qml.from_openfermion(of_fermionic) 
>>> type(pl_fermionic) 
<class 'pennylane.fermi.fermionic.FermiWord'> 
>>> print(pl_fermionic) 
a⁺(0) a(2)

And for qubit operators:

>>> of_qubit = 0.5 * openfermion.QubitOperator('X0 X5') 
>>> pl_qubit = qml.from_openfermion(of_qubit) 
>>> print(pl_qubit) 
0.5 * (X(0) @ X(5))

Better control over when drawing and specs take place 🎚️

It is now possible to control the stage at which qml.draw, qml.draw_mpl, and qml.specs occur within a QNode's transform program. (#5855) (#5781)

Consider the following circuit which has multiple transforms applied:

@qml.transforms.split_non_commuting 
@qml.transforms.cancel_inverses 
@qml.transforms.merge_rotations 
@qml.qnode(qml.device("default.qubit")) 
def f(): 
    qml.Hadamard(0) 
    qml.Y(0) 
    qml.RX(0.4, 0) 
    qml.RX(-0.4, 0) 
    qml.Y(0) 
    return qml.expval(qml.X(0) + 2 * qml.Y(0))

We can specify a level value when using qml.draw():

>>> print(qml.draw(f, level=0)()) # input program 
0: ──H──Y──RX(0.40)──RX(-0.40)──Y─┤ <X+(2.00*Y)> 
>>> print(qml.draw(f, level=1)()) # rotations merged 
0: ──H──Y──Y─┤ <X+(2.00*Y)> 
>>> print(qml.draw(f, level=2)()) # inverses cancelled 
0: ──H─┤ <X+(2.00*Y)> 
>>> print(qml.draw(f, level=3)()) # Hamiltonian expanded 
0: ──H─┤ <X>

0: ──H─┤ <Y>

The qml.workflow.get_transform_program function can be used to see the full transform program.

>>> qml.workflow.get_transform_program(f) 
TransformProgram(merge_rotations, cancel_inverses, split_non_commuting, validate_device_wires, mid_circuit_measurements, decompose, validate_measurements, validate_observables, no_sampling)

Note that additional transforms can be added automatically from device preprocessing or gradient calculations. Rather than providing an integer value to level, it is possible to target the "user", "gradient" or "device" stages:

n_wires = 3 
x = np.random.random((2, n_wires))

@qml.qnode(qml.device("default.qubit")) 
def f(): 
    qml.BasicEntanglerLayers(x, range(n_wires)) 
    return qml.expval(qml.X(0))

>>> print(qml.draw(f, level="device")()) 
0: ──RX(0.28)─╭●────╭X──RX(0.70)─╭●────╭X─┤ <X> 
1: ──RX(0.52)─╰X─╭●─│───RX(0.65)─╰X─╭●─│──┤ 
2: ──RX(0.00)────╰X─╰●──RX(0.03)────╰X─╰●─┤

Improvements 🛠

Community contributions, including UnitaryHACK 💛

default.clifford now supports arbitrary state-based measurements with qml.Snapshot. (#5794)
qml.equal now properly handles Pow, Adjoint, Exp, and SProd operators as arguments across different interfaces and tolerances with the addition of four new keyword arguments: check_interface, check_trainability, atol and rtol. (#5668)
The implementation for qml.assert_equal has been updated for Operator, Controlled, Adjoint, Pow, Exp, SProd, ControlledSequence, Prod, Sum, Tensor and Hamiltonian instances. (#5780) (#5877)
qml.from_qasm now supports the ability to convert mid-circuit measurements from OpenQASM 2 code, and it can now also take an optional argument to specify a list of measurements to be performed at the end of the circuit, just like qml.from_qiskit. (#5818)
Four new operators have been added for simulating noise on the default.qutrit.mixed device: (#5502) (#5793) (#5503) (#5757) (#5799) (#5784)
- qml.QutritDepolarizingChannel: a channel that adds depolarizing noise.
- qml.QutritChannel: enables the specification of noise using a collection of (3x3) Kraus matrices.
- qml.QutritAmplitudeDamping: a channel that adds noise processes modelled by amplitude damping.
- qml.TritFlip: a channel that adds trit flip errors, such as misclassification.

Faster and more flexible mid-circuit measurements

The default.qubit device supports a depth-first tree-traversal algorithm to accelerate native mid-circuit measurement execution. Accessible through the QNode argument mcm_method="tree-traversal", this new implementation supports classical control, collecting statistics, and post-selection, along with all measurements enabled with qml.dynamic_one_shot. More information about this new mid-circuit measurement method can be found on our measurement documentation page. (#5180)
qml.QNode and the @qml.qnode decorator now accept two new keyword arguments: postselect_mode and mcm_method. These keyword arguments can be used to configure how the device should behave when running circuits with mid-circuit measurements. (#5679) (#5833) (#5850)
- postselect_mode="hw-like" indicates to devices to discard invalid shots when postselecting mid-circuit measurements. Use postselect_mode="fill-shots" to unconditionally sample the postselected value, thus making all samples valid. This is equivalent to sampling until the number of valid samples matches the total number of shots.
- mcm_method will indicate which strategy to use for running circuits with mid-circuit measurements. Use mcm_method="deferred" to use the deferred measurements principle, or mcm_method="one-shot" to execute once for each shot. If qml.qjit is being used (the Catalyst compiler), mcm_method="single-branch-statistics" is also available. Using this method, a single branch of the execution tree will be randomly explored.
The dynamic_one_shot transform received a few improvements:
- dynamic_one_shot is now compatible with qml.qjit (the Catalyst compiler). (#5766) (#5888)
- dynamic_one_shot now uses a single auxiliary tape with a shot vector and default.qubit implements the loop over shots with jax.vmap. (#5617)
- dynamic_one_shot is now compatible with jax.jit. (#5557)

When using defer_measurements with postselection, operations that will never be active due to the postselected state are skipped in the transformed quantum circuit. In addition, postselected controls are skipped, as they are evaluated when the transform is applied. This optimization feature can be turned off by setting reduce_postselected=False. (#5558)

Consider a simple circuit with three mid-circuit measurements, two of which are postselecting, and a single gate conditioned on those measurements:

@qml.qnode(qml.device("default.qubit")) 
def node(x): 
    qml.RX(x, 0) 
    qml.RX(x, 1) 
    qml.RX(x, 2) 
    mcm0 = qml.measure(0, postselect=0, reset=False) 
    mcm1 = qml.measure(1, postselect=None, reset=True) 
    mcm2 = qml.measure(2, postselect=1, reset=False) 
    qml.cond(mcm0 + mcm1 + mcm2 == 1, qml.RX)(0.5, 3) 
    return qml.expval(qml.Z(0) @ qml.Z(3))

Without the new optimization, we obtain three gates, each controlled on the three measured qubits. They correspond to the combinations of controls that satisfy the condition mcm0 + mcm1 + mcm2 == 1:

>>> print(qml.draw(qml.defer_measurements(node, reduce_postselected=False))(0.6)) 
0: ──RX(0.60)──|0⟩⟨0|─╭●─────────────────────────────────────────────┤ ╭<Z@Z> 
1: ──RX(0.60)─────────│──╭●─╭X───────────────────────────────────────┤ │ 
2: ──RX(0.60)─────────│──│──│───|1⟩⟨1|─╭○────────╭○────────╭●────────┤ │ 
3: ───────────────────│──│──│──────────├RX(0.50)─├RX(0.50)─├RX(0.50)─┤ ╰<Z@Z> 
4: ───────────────────╰X─│──│──────────├○────────├●────────├○────────┤ 
5: ──────────────────────╰X─╰●─────────╰●────────╰○────────╰○────────┤

If we do not explicitly deactivate the optimization, we obtain a much simpler circuit:

>>> print(qml.draw(qml.defer_measurements(node))(0.6)) 
0: ──RX(0.60)──|0⟩⟨0|─╭●─────────────────┤ ╭<Z@Z> 
1: ──RX(0.60)─────────│──╭●─╭X───────────┤ │ 
2: ──RX(0.60)─────────│──│──│───|1⟩⟨1|───┤ │ 
3: ───────────────────│──│──│──╭RX(0.50)─┤ ╰<Z@Z> 
4: ───────────────────╰X─│──│──│─────────┤ 
5: ──────────────────────╰X─╰●─╰○────────┤

There is only one controlled gate with only one control wire.

Mid-circuit measurement tests have been streamlined and refactored, removing most end-to-end tests from the native MCM test file, but keeping one that validates multiple mid-circuit measurements with any allowed return and interface end-to-end tests. (#5787)

Access to QROM

The QROM algorithm is now available in PennyLane with qml.QROM. This template allows you to enter classical data in the form of bitstrings. (#5688)

bitstrings = ["010", "111", "110", "000"]

dev = qml.device("default.qubit", shots = 1)

@qml.qnode(dev) 
def circuit(): 
    qml.BasisEmbedding(2, wires = [0,1])

qml.QROM(bitstrings = bitstrings, control_wires = [0,1], target_wires = [2,3,4], work_wires = [5,6,7])

return qml.sample(wires = [2,3,4])

>>> print(circuit()) 
[1 1 0]

Capturing and representing hybrid programs

A number of templates have been updated to be valid PyTrees and PennyLane operations. (#5698)
PennyLane operators, measurements, and QNodes can now automatically be captured as instructions in JAXPR. (#5564) (#5511) (#5708) (#5523) (#5686) (#5889)
The qml.PyTrees module now has flatten and unflatten methods for serializing PyTrees. (#5701)
qml.sample can now be used on Boolean values representing mid-circuit measurement results in traced quantum functions. This feature is used with Catalyst to enable the pattern m = measure(0); qml.sample(m). (#5673)

Quantum chemistry

The qml.qchem.Molecule object received a few improvements:
- qml.qchem.Molecule is now the central object used by all qchem functions. (#5571)
- qml.qchem.Molecule now supports Angstrom as a unit. (#5694)
- qml.qchem.Molecule now supports open-shell systems. (#5655)
The qml.qchem.molecular_hamiltonian function now supports parity and Bravyi-Kitaev mappings. (#5657)
qml.qchem.molecular_dipole function has been added for calculating the dipole operator using the "dhf" and "openfermion" backends. (#5764)
The qchem module now has dedicated functions for calling the pyscf and openfermion backends and the molecular_hamiltonian and molecular_dipole functions have been moved to hamiltonian and dipole modules. (#5553) (#5863)
More fermionic-to-qubit tests have been added to cover cases when the mapped operator is different for various mapping schemes. (#5873)

Easier development

Logging now allows for an easier opt-in across the stack and support has been extended to Catalyst. (#5528)
Three new Pytest markers have been added for easier management of our test suite: unit, integration and system. (#5517)

Other improvements

qml.MultiControlledX can now be decomposed even when no work_wires are provided. The implementation returns $\mathcal{O}(\mbox{len(control wires)}^2)$ operations and is applicable for any multi-controlled unitary gate. This decomposition is provided in arXiv:quant-ph/9503016. (#5735)

A new function called expectation_value has been added to qml.math to calculate the expectation value of a matrix for pure states. (#4484)

>>> state_vector = [1/np.sqrt(2), 0, 1/np.sqrt(2), 0] 
>>> operator_matrix = qml.matrix(qml.PauliZ(0), wire_order=[0,1]) 
>>> qml.math.expectation_value(operator_matrix, state_vector) 
tensor(-2.23711432e-17+0.j, requires_grad=True)

param_shift with the broadcast=True option now supports shot vectors and multiple measurements. (#5667)
qml.TrotterProduct is now compatible with resource tracking by inheriting from ResourcesOperation. (#5680)
packaging is now a required package in PennyLane. (#5769)
qml.ctrl now works with tuple-valued control_values when applied to any already controlled operation. (#5725)
The sorting order of parameter-shift terms is now guaranteed to resolve ties in the absolute value with the sign of the shifts. (#5582)
qml.transforms.split_non_commuting can now handle circuits containing measurements of multi-term observables. (#5729) (#5838) (#5828) (#5869) (#5939) (#5945)
qml.devices.LegacyDevice is now an alias for qml.Device, so it is easier to distinguish it from qml.devices.Device, which follows the new device API. (#5581)
The dtype for eigvals of X, Y, Z and Hadamard is changed from int to float, making them consistent with the other observables. The dtype of the returned values when sampling these observables (e.g. qml.sample(X(0))) is also changed to float. (#5607)
The framework for the development of an assert_equal function for testing operator comparison has been set up. (#5634) (#5858)
The decompose transform has an error keyword argument to specify the type of error that should be raised, allowing error types to be more consistent with the context the decompose function is used in. (#5669)
Empty initialization of PauliVSpace is permitted. (#5675)
qml.tape.QuantumScript properties are only calculated when needed, instead of on initialization. This decreases the classical overhead by over 20%. Also, par_info, obs_sharing_wires, and obs_sharing_wires_id are now public attributes. (#5696)
The qml.data module now supports PyTree data types as dataset attributes (#5732)
qml.ops.Conditional now inherits from qml.ops.SymbolicOp, thus it inherits several useful common functionalities. Other properties such as adjoint and diagonalizing gates have been added using the base properties. (##5772)
New dispatches for qml.ops.Conditional and qml.MeasurementValue have been added to qml.equal. (##5772)
The qml.snapshots transform now supports arbitrary devices by running a separate tape for each snapshot for unsupported devices. (#5805)
The qml.Snapshot operator now accepts sample-based measurements for finite-shot devices. (#5805)
Device preprocess transforms now happen inside the ML boundary. (#5791)
Transforms applied to callables now use functools.wraps to preserve the docstring and call signature of the original function. (#5857)
qml.qsvt() now supports JAX arrays with angle conversions. (#5853)
The sorting order of parameter-shift terms is now guaranteed to resolve ties in the absolute value with the sign of the shifts. (#5583)

Breaking changes 💔

Passing shots as a keyword argument to a QNode initialization now raises an error instead of ignoring the input. (#5748)
A custom decomposition can no longer be provided to qml.QDrift. Instead, apply the operations in your custom operation directly with qml.apply. (#5698)
Sampling observables composed of X, Y, Z and Hadamard now returns values of type float instead of int. (#5607)
qml.is_commuting no longer accepts the wire_map argument, which does not bring any functionality. (#5660)
qml.from_qasm_file has been removed. The user can open files and load their content using qml.from_qasm. (#5659)
qml.load has been removed in favour of more specific functions, such as qml.from_qiskit, etc. (#5654)
qml.transforms.convert_to_numpy_parameters is now a proper transform and its output signature has changed, returning a list of QuantumScripts and a post-processing function instead of simply the transformed circuit. (#5693)
Controlled.wires does not include self.work_wires anymore. That can be accessed separately through Controlled.work_wires. Consequently, Controlled.active_wires has been removed in favour of the more common Controlled.wires. (#5728)

Deprecations 👋

The simplify argument in qml.Hamiltonian and qml.ops.LinearCombination has been deprecated. Instead, qml.simplify() can be called on the constructed operator. (#5677)
qml.transforms.map_batch_transform has been deprecated, since a transform can be applied directly to a batch of tapes. (#5676)
The default behaviour of qml.from_qasm() to remove measurements in the QASM code has been deprecated. Use measurements=[] to keep this behaviour or measurements=None to keep the measurements from the QASM code. (#5882) (#5904)

Documentation 📝

The qml.qchem docs have been updated to showcase the new improvements. (#5758) (#5638)
Several links to other functions in measurement process docstrings have been fixed. (#5913)
Information about mid-circuit measurements has been moved from the measurements quickstart page to its own mid-circuit measurements quickstart page (#5870)
The documentation for the default.tensor device has been added. (#5719)
A small typo was fixed in the docstring for qml.sample. (#5685)
Typesetting for some of the documentation was fixed, (use of left/right delimiters, fractions, and fixing incorrectly set up commands) (#5804)
The qml.Tracker examples have been updated. (#5803)
The input types for coupling_map in qml.transpile have been updated to reflect all the allowed input types by nx.to_networkx_graph. (#5864)
The text in the qml.data module and datasets quickstart has been slightly modified to lead to the quickstart first and highlight list_datasets. (5484)

Bug fixes 🐛

qml.compiler.active first checks whether Catalyst is imported at all to avoid changing jax_enable_x64 on module initialization. (#5960)
The __invert__ dunder method of the MeasurementValue class uses an array-valued function. (#5955)
Skip Projector-measurement tests on devices that do not support it. (#5951)
The default.tensor device now preserves the order of wires if the initial MPS is created from a dense state vector. (#5892)
Fixed a bug where hadamard_grad returned a wrong shape for qml.probs() without wires. (#5860)
An error is now raised on processing an AnnotatedQueue into a QuantumScript if the queue contains something other than an Operator, MeasurementProcess, or QuantumScript. (#5866)
Fixed a bug in the wire handling on special controlled ops. (#5856)
Fixed a bug where Sum's with repeated identical operations ended up with the same hash as Sum's with different numbers of repeats. (#5851)
qml.qaoa.cost_layer and qml.qaoa.mixer_layer can now be used with Sum operators. (#5846)
Fixed a bug where qml.MottonenStatePreparation produces wrong derivatives at special parameter values. (#5774)
Fixed a bug where fractional powers and adjoints of operators were commuted, which is not well-defined/correct in general. Adjoints of fractional powers can no longer be evaluated. (#5835)
qml.qnn.TorchLayer now works with tuple returns. (#5816)
An error is now raised if a transform is applied to a catalyst qjit object. (#5826)
qml.qnn.KerasLayer and qml.qnn.TorchLayer no longer mutate the input qml.QNode's interface. (#5800)
Docker builds on PR merging has been disabled. (#5777)
The validation of the adjoint method in DefaultQubit correctly handles device wires now. (#5761)
QuantumPhaseEstimation.map_wires on longer modifies the original operation instance. (#5698)
The decomposition of qml.AmplitudeAmplification now correctly queues all operations. (#5698)
Replaced semantic_version with packaging.version.Version, since the former cannot handle the metadata .post in the version string. (#5754)
The dynamic_one_shot transform now has expanded support for the jax and torch interfaces. (#5672)
The decomposition of StronglyEntanglingLayers is now compatible with broadcasting. (#5716)
qml.cond can now be applied to ControlledOp operations when deferring measurements. (#5725)
The legacy Tensor class can now handle a Projector with abstract tracer input. (#5720)
Fixed a bug that raised an error regarding expected versus actual dtype when using JAX-JIT on a circuit that returned samples of observables containing the qml.Identity operator. (#5607)
The signature of CaptureMeta objects (like Operator) now match the signature of the __init__ call. (#5727)
Vanilla NumPy arrays are now used in test_projector_expectation to avoid differentiating qml.Projector with respect to the state attribute. (#5683)
qml.Projector is now compatible with jax.jit. (#5595)
Finite-shot circuits with a qml.probs measurement, both with a wires or op argument, can now be compiled with jax.jit. (#5619)
param_shift, finite_diff, compile, insert, merge_rotations, and transpile now all work with circuits with non-commuting measurements. (#5424) (#5681)
A correction has been added to qml.bravyi_kitaev to call the correct function for a qml.FermiSentence input. (#5671)
Fixed a bug where sum_expand produces incorrect result dimensions when combined with shot vectors, multiple measurements, and parameter broadcasting. (#5702)
Fixed a bug in qml.math.dot that raises an error when only one of the operands is a scalar. (#5702)
qml.matrix is now compatible with QNodes compiled by qml.qjit. (#5753)
qml.snapshots raises an error when a measurement other than qml.state is requested from default.qubit.legacy instead of silently returning the statevector. (#5805)
Fixed a bug where default.qutrit was falsely determined to be natively compatible with qml.snapshots. (#5805)
Fixed a bug where the measurement of a qml.Snapshot instance was not passed on during the qml.adjoint and qml.ctrl operations. (#5805)
qml.CNOT and qml.Toffoli now have an arithmetic_depth of 1, as they are controlled operations. (#5797)
Fixed a bug where the gradient of ControlledSequence, Reflection, AmplitudeAmplification, and Qubitization was incorrect on default.qubit.legacy with parameter_shift. (#5806)
Fixed a bug where split_non_commuting raises an error when the circuit contains measurements of observables that are not Pauli words. (#5827)
The simplify method for qml.Exp now returns an operator with the correct number of Trotter steps, i.e. equal to the one from the pre-simplified operator. (#5831)
Fixed a bug where CompositeOp.overlapping_ops would put overlapping operators in different groups, leading to incorrect results returned by LinearCombination.eigvals(). (#5847)
The correct decomposition for a qml.PauliRot with an identity as pauli_word has been implemented, i.e. returns a qml.GlobalPhase with half the angle. (#5875)
qml.pauli_decompose now works in a jit-ted context, such as jax.jit and qml.qjit. (#5878)

Contributors ✍️

This release contains contributions from (in alphabetical order):

Tarun Kumar Allamsetty, Guillermo Alonso-Linaje, Utkarsh Azad, Lillian M. A. Frederiksen, Ludmila Botelho, Gabriel Bottrill, Thomas Bromley, Jack Brown, Astral Cai, Ahmed Darwish, Isaac De Vlugt, Diksha Dhawan, Pietropaolo Frisoni, Emiliano Godinez, Diego Guala, Daria Van Hende, Austin Huang, David Ittah, Soran Jahangiri, Rohan Jain, Mashhood Khan, Korbinian Kottmann, Christina Lee, Vincent Michaud-Rioux, Lee James O'Riordan, Mudit Pandey, Kenya Sakka, Jay Soni, Kazuki Tsuoka, Haochen Paul Wang, David Wierichs.

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Release 0.37.0

Release 0.37.0

New features since last release

Execute wide circuits with Default Tensor 🔗

Add noise models to your quantum circuits 📺

Catch bugs with the PennyLane debugger 🚫🐞

Convert between OpenFermion and PennyLane 🤝

Better control over when drawing and specs take place 🎚️

Improvements 🛠

Community contributions, including UnitaryHACK 💛

Faster and more flexible mid-circuit measurements

Access to QROM

Capturing and representing hybrid programs

Quantum chemistry

Easier development

Other improvements

Breaking changes 💔

Deprecations 👋

Documentation 📝

Bug fixes 🐛

Contributors ✍️