Getting Started#

The tket compiler is a powerful tool for optimizing and manipulating platform-agnostic quantum circuits, focused on enabling superior performance on NISQ (noisy intermediate-scale quantum) devices. The pytket package provides an API for interacting with tket and transpiling to and from other popular quantum circuit specifications.

Pytket is compatible with 64-bit Python 3.9, 3.10 and 3.11, on Linux, MacOS (11.0 or later) and Windows. Install pytket from PyPI using:

pip install pytket

This will install the tket compiler binaries as well as the pytket package. For those using an older version of pytket, keep up to date by installing with the --upgrade flag for additional features and bug fixes.

There are separate packages for managing the interoperability between pytket and other quantum software packages which can also be installed via PyPI. For details of these, see the pytket-extensions documentation.

The quantum circuit is an abstraction of computation using quantum resources, designed by initializing a system into a fixed state, then mutating it via sequences of instructions (gates).

The native circuit interface built into pytket allows us to build circuits and use them directly.

from pytket import Circuit

c = Circuit(2, 2) # define a circuit with 2 qubits and 2 bits
c.H(0)            # add a Hadamard gate to qubit 0
c.Rz(0.25, 0)     # add an Rz gate of angle 0.25*pi to qubit 0
c.CX(1,0)         # add a CX gate with control qubit 1 and target qubit 0
c.measure_all()   # measure qubits 0 and 1, recording the results in bits 0 and 1

Pytket provides many handy shortcuts and higher-level components for building circuits, including custom gate definitions, circuit composition, gates with symbolic parameters, and conditional gates.

On the other hand, pytket’s flexibile interface allows you to take circuits defined in a number of languages, including raw source code languages such as OpenQASM and Quipper, or embedded python frameworks such as Qiskit and Cirq.

from pytket.qasm import circuit_from_qasm

c = circuit_from_qasm("my_qasm_file.qasm")

Or, if an extension module like pytket-qiskit is installed:

from qiskit import QuantumCircuit
from pytket.extensions.qiskit import qiskit_to_tk

qc = QuantumCircuit()
# ...
c = qiskit_to_tk(qc)

See the pytket user manual for an extensive tutorial on pytket, providing a gentle introduction to its features and how to run circuits on backend devices, with worked examples.

In pytket there is also a generic Backend interface. This represents a connection to a quantum device or simulator. It’s possible to run circuits on platforms from different providers through the extension modules.

from pytket import Circuit
from pytket.extensions.qiskit import AerBackend

# Define Circuit
circ = Circuit(3)
circ.H(0).CX(0, 1).CX(0, 2)

# Initialise Backend and execute the Circuit
backend = AerBackend()
result = backend.run_circuit(circ, n_shots=1000)

This prints out a summary of readouts (the final values of the classical bits) and their frequencies.

Each pytket Backend comes with its own default compilation method. This is a recommended sequence of optimisation passes to meet the requirements of the specific Backend.

The following code snippet will show how to compile a circuit to run on an IBM device. This requires setting up IBM credentials (see the credentials guide).

from pytket.extensions.qiskit import IBMQBackend

circ = Circuit(3).X(0).CCX(0, 1, 2)
belem_device = IBMQBackend('ibmq_belem')

# Compile Circuit to use supported gates of IBMQ Belem
compiled_circ = belem_device.get_compiled_circuit(circ)
result = backend.run_circuit(compiled_circ, n_shots=100)

Here the default compilation pass is applied by IBMQBackend.get_compiled_circuit(). See this page for more details.

As an alternative, We can experiment with constructing our own circuit compilation routines in pytket. Passes from the pytket.passes module can be applied individually or composed in sequence. See the section of the user manual on circuit compilation and the corresponding notebook example for more.