Quantum Information Software Kit (QISKit), SDK Python version for working with OpenQASM and the IBM Q experience (QX).
QISKit is a collection of software for working with short depth quantum circuits and building near term applications and experiments on quantum computers. In QISKit, a quantum program is an array of quantum circuits. The program workflow consists of three stages: Build, Compile, and Run. Build allows you to make different quantum circuits that represent the problem you are solving; Compile allows you to rewrite them to run on different backends (simulators/real chips of different quantum volumes, sizes, fidelity, etc); and Run launches the jobs. After the jobs have been run, the data is collected. There are methods for putting this data together, depending on the program. This either gives you the answer you wanted or allows you to make a better program for the next instance.
The QISKit project comprises:
- QISKit SDK: Provides support for the Quantum Experience circuit generation phase and lets you use the QISKit API to access the Quantum Experience hardware and simulators. The SDK also includes example scripts written for Jupyter Notebooks.
- QISKit API: A thin Python wrapper around the Quantum Experience HTTP API that enables you to connect and and execute OpenQASM code.
- QISKit OpenQASM: Contains specifications, examples, documentation, and tools for the OpenQASM intermediate representation.
The starting point for writing code is the QuantumProgram object. The QuantumProgram is a collection of circuits, or scores if you are coming from the Quantum Experience, quantum register objects, and classical register objects. The QuantumProgram methods can send these circuits to quantum hardware or simulator backends and collect the results for further analysis.
To compose and run a circuit on a simulator, which is distributed with this project, one can do,
from qiskit import QuantumProgram
qp = QuantumProgram()
qr = qp.create_quantum_register('qr', 2)
cr = qp.create_classical_register('cr', 2)
qc = qp.create_circuit('Bell', [qr], [cr])
qc.h(qr[0])
qc.cx(qr[0], qr[1])
qc.measure(qr[0], cr[0])
qc.measure(qr[1], cr[1])
result = qp.execute('Bell')
print(result.get_counts('Bell'))The get_counts method outputs a dictionary of state:counts pairs;
{'00': 531, '11': 493}Python example programs can be found in the examples directory, and test scripts are located in test. The qiskit directory is the main module of the SDK.
The qiskit directory is the main Python module and contains the programming interface objects QuantumProgram, QuantumRegister, ClassicalRegister, and QuantumCircuit.
At the highest level, users construct a QuantumProgram to create, modify, compile, and execute a collection of quantum circuits. Each QuantumCircuit has a set of data registers, each of type QuantumRegister or ClassicalRegister. Methods of these objects are used to apply instructions that define the circuit. The QuantumCircuit can then generate OpenQASM code that can flow through other components in the qiskit directory.
The extensions directory extends quantum circuits as needed to support other gate sets and algorithms. Currently there is a standard extension defining some typical quantum gates.
The directory also contains internal modules that are still under development:
- a qasm module for parsing OpenQASM circuits
- an unroll module to interpret and “unroll” OpenQASM to a target gate basis (expanding gate subroutines and loops as needed)
- a dagcircuit module for working with circuits as graphs
- a mapper module for mapping all-to-all circuits to run on devices with fixed couplings
- a simulators module contains quantum circuit simulators
- a tools directory contains methods for applications, analysis, and visualization
Quantum circuits flow through the components as follows. The programming interface is used to generate OpenQASM circuits, as text or QuantumCircuit objects. OpenQASM source, as a file or string, is passed into a Qasm object, whose parse method produces an abstract syntax tree (AST). The AST is passed to an Unroller that is attached to an UnrollerBackend. There is a PrinterBackend for outputting text, a JsonBackend for producing input to simulator and experiment backends, a DAGBackend for constructing DAGCircuit objects, and a CircuitBackend for producing QuantumCircuit objects. The DAGCircuit object represents an “unrolled” OpenQASM circuit as a directed acyclic graph (DAG). The DAGCircuit provides methods for representing, transforming, and computing properties of a circuit and outputting the results again as OpenQASM. The whole flow is used by the mapper module to rewrite a circuit to execute on a device with fixed couplings given by a CouplingGraph. The structure of these components is subject to change.
The circuit representations and how they are currently transformed into each other are summarized in this figure:
Several unroller backends and their outputs are summarized here:
