# Changelog¶

## v2.5 (March 6, 2019)¶

Improvements and Changes:

- PyQuil’s Gate objects now expose
`.controlled(q)`

and`.dagger()`

modifiers, which turn a gate respectively into its controlled variant, conditional on the qubit`q`

, or into its inverse. - The operator estimation suite’s
`measure_observables`

method now exposes a`readout_symmetrize`

argument, which helps mitigate a machine’s fidelity asymmetry between recognizing a qubit in the ground state versus the excited state. - The
`MEASURE`

instruction in pyQuil now has a*mandatory*second argument. Previously, the second argument could be omitted to induce “measurement for effect”, without storing the readout result to a classical register, but users found this to be a common source of accidental error and a generally rude surprise. To ensure the user really intends to measure only for effect, we now require that they supply an explicit`None`

as the second argument.

Bugfixes:

- Some stale tests have been brought into the modern era.

## v2.4 (February 14, 2019)¶

Announcements:

- The Quil Compiler (quilc) and
the Quantum Virtual Machine (QVM),
which are part of the Forest SDK, have been open sourced! In addition to
downloading the binaries, you can now build these applications locally from source,
or run them via the Docker images rigetti/quilc
and rigetti/qvm. These Docker images are now
used as the
`services`

in the GitLab CI build plan YAML (gh-792, gh-794, gh-795).

Improvements and Changes:

- The
`WavefunctionSimulator`

now supports the use of parametric Quil programs, via the`memory_map`

parameter for its various methods (gh-787). - Operator estimation data structures introduced in
**v2.2**have changed. Previously,`ExperimentSettings`

had two members:`in_operator`

and`out_operator`

. The`out_operator`

is unchanged, but`in_operator`

has been renamed to`in_state`

and its data type is now`TensorProductState`

instead of`PauliTerm`

. It was always an abuse of notation to interpret pauli operators as defining initial states. Analogous to the Pauli helper functions sI, sX, sY, and sZ,`TensorProductState`

objects are constructed by multiplying together terms generated by the helper functions plusX, minusX, plusY, minusY, plusZ, and minusZ. This functionality enables process tomography and process DFE (gh-770). - Operator estimation now offers a “greedy” method for grouping tomography-like experiments that share a natural tensor product basis (ntpb), as an alternative to the clique cover version (gh-754).
- The
`quilc`

endpoint for rewriting Quil parameter arithmetic has been changed from`resolve_gate_parameter_arithmetic`

to`rewrite_arithmetic`

(gh-802). - The difference between ProtoQuil and QPU-supported Quil is now better defined (gh-798).

Bugfixes:

- Resolved an issue with post-gate noise in the pyQVM (gh-801).
- A
`TypeError`

with a useful error message is now raised when a`Program`

object is run on a QPU-backed`QuantumComputer`

, rather than a confusing`AttributeError`

(gh-799).

## v2.3 (January 28, 2019)¶

PyQuil 2.3 is the latest release of pyQuil, Rigetti’s toolkit for constructing and running quantum programs. A major new feature is the release of a new suite of simulators:

- We’re proud to introduce the first iteration of a Python-based quantum virtual machine (QVM)
called PyQVM. This QVM is completely contained within pyQuil and does not need any external
dependencies. Try using it with
`get_qc("9q-square-pyqvm")`

or explore the`pyquil.pyqvm.PyQVM`

object directly. Under-the-hood, there are three quantum simulator backends:`ReferenceWavefunctionSimulator`

uses standard matrix-vector multiplication to evolve a statevector. This includes a suite of tools in`pyquil.unitary_tools`

for dealing with unitary matrices.`NumpyWavefunctionSimulator`

uses numpy’s tensordot functionality to efficiently evolve a statevector. For most simulations, performance is quite good.`ReferenceDensitySimulator`

uses matrix-matrix multiplication to evolve a density matrix.

- Matrix representations of Quil standard gates are included in
`pyquil.gate_matrices`

(gh-552). - The density simulator has extremely limited support for Kraus-operator based noise models. Let us know if you’re interested in contributing more robust noise-model support.
- This functionality should be considered experimental and may undergo minor API changes.

Important changes to note:

- Quil math functions (like COS, SIN, …) used to be ambiguous with respect to case sensitivity. They are now case-sensitive and should be uppercase (gh-774).
- In the next release of pyQuil, communication with quilc will happen exclusively via the rpcq
protocol.
`LocalQVMCompiler`

and`LocalBenchmarkConnection`

will be removed in favor of a unified`QVMCompiler`

and`BenchmarkConnection`

. This change should be transparent if you use`get_qc`

and`get_benchmarker`

, respectively. In anticipation of this change we recommend that you upgrade your version of quilc to 1.3, released Jan 30, 2019 (gh-730). - When using a paramaterized gate, the QPU control electronics only allowed multiplying
parameters by powers of two. If you only ever multiply a parameter by the same constant,
this isn’t too much of a problem because you can fold the multiplicative constant
into the definition of the parameter. However, if you are multiplying the same variable
(e.g.
`gamma`

in QAOA) by different constants (e.g. weighted maxcut edge weights) it doesn’t work. PyQuil will now transparently handle the latter case by expanding to a vector of parameters with the constants folded in, allowing you to multiply variables by whatever you want (gh-707).

As always, this release contains bug fixes and improvements:

- The CZ gate fidelity metric available in the Specs object now has its associated standard
error, which is accessible from the method
`Specs.fCZ_std_errs`

(gh-751). - Operator estimation code now correctly handles identity terms with coefficients. Previously, it would always estimate these terms as 1.0 (gh-758).
- Operator estimation results include the total number of counts (shots) taken.
- Operator estimation JSON serialization uses utf-8. Please let us know if this causes problems (gh-769).
- The example quantum die program now can roll dice that are not powers of two (gh-749).
- The teleportation and Meyer penny game examples had a syntax error (gh-778, gh-772).
- When running on the QPU, you could get into trouble if the QPU name passed to
`get_qc`

did not match the lattice you booked. This is now validated (gh-771).

We extend thanks to community member estamm12 for their contribution to this release.

## v2.2 (January 4, 2019)¶

PyQuil 2.2 is the latest release of pyQuil, Rigetti’s toolkit for constructing and running quantum programs. Bug fixes and improvements include:

`pauli.is_zero`

and`paulis.is_identity`

would sometimes return erroneous answers (gh-710).- Parameter expressions involving addition and subtraction are now converted to Quil with spaces
around the operators, e.g.
`theta + 2`

instead of`theta+2`

. This disambiguates subtracting two parameters, e.g.`alpha - beta`

is not one variable named`alpha-beta`

(gh-743). - T1 is accounted for in T2 noise models (gh-745).
- Documentation improvements (gh-723, gh-719, gh-720, gh-728, gh-732, gh-742).
- Support for PNG generation of circuit diagrams via LaTeX (gh-745).
- We’ve started transitioning to using Gitlab as our continuous integration provider for pyQuil (gh-741, gh-752).

This release includes a new module for facilitating the estimation of quantum observables/operators (gh-682). First-class support for estimating observables should make it easier to express near-term algorithms. This release includes:

- data structures for expressing tomography-like experiments and their results
- grouping of experiment settings that can be simultaneously estimated
- functionality to executing a tomography-like experiment on a quantum computer

Please look forward to more features and polish in future releases. Don’t hesitate to submit feedback or suggestions as GitHub issues.

We extend thanks to community member petterwittek for their contribution to this release.

Bugfix release 2.2.1 was released January 11 to maintain compatibility with the latest version of the quilc compiler (gh-759).

## v2.1 (November 30, 2018)¶

PyQuil 2.1 is an incremental release of pyQuil, Rigetti’s toolkit for constructing and running quantum programs. Changes include:

- Major documentation improvements.
`QuantumComputer.run()`

accepts an optional`memory_map`

parameter to facilitate running parametric executables (gh-657).`QuantumComputer.reset()`

will reset the state of a QAM to recover from an error condition (gh-703).- Bug fixes (gh-674, gh-696).
- Quil parser improvements (gh-689, gh-685).
- Optional interleaver argument when generating RB sequences (gh-673).
- Our GitHub organization name has changed from
`rigetticomputing`

to`rigetti`

(gh-713).

## v2.0 (November 1, 2018)¶

PyQuil 2.0 is a major release of pyQuil, Rigetti’s toolkit for constructing and running quantum programs. This release contains many major changes including:

- The introduction of Quantum Cloud Services. Access Rigetti’s QPUs from co-located classical compute resources for minimal latency. The web API for running QVM and QPU jobs has been deprecated and cannot be accessed with pyQuil 2.0
- Advances in classical control systems and compilation allowing the pre-compilation of parametric binary executables for rapid hybrid algorithm iteration.
- Changes to Quil—our quantum instruction language—to provide easier ways of interacting with classical memory.

The new QCS access model and features will allow you to execute hybrid quantum algorithms several orders of magnitude (!) faster than the previous web endpoint. However, to fully exploit these speed increases you must update your programs to use the latest pyQuil features and APIs. Please read New in Forest 2 - Other for a comprehensive migration guide.

An incomplete list of significant changes:

- Python 2 is no longer supported. Please use Python 3.6+
- Parametric gates are now normal functions. You can no longer write
`RX(pi/2)(0)`

to get a Quil`RX(pi/2) 0`

instruction. Just use`RX(pi/2, 0)`

. - Gates support keyword arguments, so you can write
`RX(angle=pi/2, qubit=0)`

. - All
`async`

methods have been removed from`QVMConnection`

and`QVMConnection`

is deprecated.`QPUConnection`

has been removed in accordance with the QCS access model. Use`pyquil.get_qc()`

as the primary means of interacting with the QVM or QPU. `WavefunctionSimulator`

allows unfettered access to wavefunction properties and routines. These methods and properties previously lived on`QVMConnection`

and have been deprecated there.- Classical memory in Quil must be declared with a name and type. Please read New in Forest 2 - Other for more.
- Compilation has changed. There are now different
`Compiler`

objects that target either the QPU or QVM. You**must**explicitly compile your programs to run on a QPU or a realistic QVM.

Version 2.0.1 was released on November 9, 2018 and includes documentation changes only. This release is only available as a git tag. We have not pushed a new package to PyPI.

## v1.9 (June 6, 2018)¶

We’re happy to announce the release of pyQuil 1.9. PyQuil is Rigetti’s toolkit for constructing and running quantum programs. This release is the latest in our series of regular releases, and it’s filled with convenience features, enhancements, bug fixes, and documentation improvements.

Special thanks to community members sethuiyer, vtomole, rht, akarazeev, ejdanderson, markf94, playadust, and kadora626 for contributing to this release!

### Qubit placeholders¶

One of the focuses of this release is a re-worked concept of “Qubit Placeholders”. These are
logical qubits that can be used to construct programs. Now, a program containing qubit placeholders
must be “addressed” prior to running on a QPU or QVM. The addressing stage involves mapping
each qubit placeholder to a physical qubit (represented as an integer). For example, if you have
a 3 qubit circuit that you want to run on different sections of the Agave chip, you now can
prepare one Program and address it to many different subgraphs of the chip topology.
Check out the `QubitPlaceholder`

example notebook for more.

To support this idea, we’ve refactored parts of Pyquil to remove the assumption that qubits
can be “sorted”. While true for integer qubit labels, this probably isn’t true in general.
A notable change can be found in the construction of a `PauliSum`

: now terms will stay in the
order they were constructed.

`PauliTerm`

now remembers the order of its operations.`sX(1)*sZ(2)`

will compile to different Quil code than`sZ(2)*sX(1)`

, although the terms will still be equal according to the`__eq__`

method. During`PauliSum`

combination of like terms, a warning will be emitted if two terms are combined that have different orders of operation.`PauliTerm.id()`

takes an optional argument`sort_ops`

which defaults to True for backwards compatibility. However, this function should not be used for comparing term-type like it has been used previously. Use`PauliTerm.operations_as_set()`

instead. In the future,`sort_ops`

will default to False and will eventually be removed.`Program.alloc()`

has been deprecated. Please instantiate`QubitPlaceholder()`

directly or request a “register” (list) of`n`

placeholders by using the class constructor`QubitPlaceholder.register(n)()`

.- Programs must contain either (1) all instantiated qubits with integer indexes or (2) all
placeholder qubits of type
`QubitPlaceholder`

. We have found that most users use (1) but (2) will become useful with larger and more diverse devices. - Programs that contain qubit placeholders must be
**explicitly addressed**prior to execution. Previously, qubits would be assigned “under the hood” to integers 0…N. Now, you must use`address_qubits()`

which returns a new program with all qubits indexed depending on the`qubit_mapping`

argument. The original program is unaffected and can be “readdressed” multiple times. `PauliTerm`

can now accept`QubitPlaceholder`

in addition to integers.`QubitPlaceholder`

is no longer a subclass of`Qubit`

.`LabelPlaceholder`

is no longer a subclass of`Label`

.`QuilAtom`

subclasses’ hash functions have changed.

### Randomized benchmarking sequence generation¶

Pyquil now includes support for performing a simple benchmarking routine - randomized
benchmarking. There is a new method in the `CompilerConnection`

that will return
sequences of pyquil programs, corresponding to elements of the Clifford group. These programs
are uniformly randomly sampled, and have the property that they compose to the identity. When
concatenated and run as one program, these programs can be used in a procedure called randomized
benchmarking to gain insight about the fidelity of operations on a QPU.

In addition, the `CompilerConnection`

has another new method,
`apply_clifford_to_pauli()`

which conjugates `PauliTerms`

by
`Program`

that are composed of Clifford gates. That is to say, given a circuit C,
that contains only gates corresponding to elements of the Clifford group, and a tensor product of
elements P, from the Pauli group, this method will compute $PCP^{dagger}$. Such a procedure can
be used in various ways. An example is predicting the effect a Clifford circuit will have on an
input state modeled as a density matrix, which can be written as a sum of Pauli matrices.

### Ease of Use¶

This release includes some quality-of-life improvements such as the ability to initialize
programs with generator expressions, sensible defaults for `Program.measure_all()`

,
and sensible defaults for `classical_addresses`

in `run()`

methods.

`Program`

can be initiated with a generator expression.`Program.measure_all()`

(with no arguments) will measure all qubits in a program.`classical_addresses`

is now optional in QVM and QPU`run()`

methods. By default, any classical addresses targeted by`MEASURE`

will be returned.`QVMConnection.pauli_expectation()`

accepts`PauliSum`

as arguments. This offers a more sensible API compared to`QVMConnection.expectation()`

.- pyQuil will now retry jobs every 10 seconds if the QPU is re-tuning.
`CompilerConnection.compile()`

now takes an optional argument`isa`

that allows per-compilation specification of the target ISA.- An empty program will trigger an exception if you try to run it.

### Supported versions of Python¶

We strongly support using Python 3 with Pyquil. Although this release works with Python 2, we are dropping official support for this legacy language and moving to community support for Python 2. The next major release of Pyquil will introduce Python 3.5+ only features and will no longer work without modification for Python 2.

### Bug fixes¶

`shift_quantum_gates`

has been removed. Users who relied on this functionality should use`QubitPlaceholder`

and`address_qubits()`

to achieve the same result. Users should also double-check data resulting from use of this function as there were several edge cases which would cause the shift to be applied incorrectly resulting in badly-addressed qubits.- Slightly perturbed angles when performing RX gates under a Kraus noise model could result in incorrect behavior.
- The quantum die example returned incorrect values when
`n = 2^m`

.