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Hardware backends

Introduction

Quantum Inspire has two quantum hardware chips or quantum processors. Running algorithms on quantum chips is in some ways different from using emulators. In emulators you usually have more options to do things which you cannot (yet) do with actual hardware. In this section we describe some general restrictions of quantum chips and some background information that helps you understand how to get the most out of the chips and how to interpret the results. Some more backend-specific information and/or restrictions are given here:

A general description of the two backends can be found here:

Algorithm execution

When you run a quantum algorithm on a hardware backend you will finalize the algorithm with a measurement on one or more qubits in order to get the results of the measurement in the binary register. In most cases you will need to execute multiple shots in order to get some statistics on your measurement and to reduce the effects of decoherence, leakage and control imperfections. On a hardware backend, when you execute multiple shots of your algorithm, all of them will be executed back to back. For each shot, the final measurement results will be stored in the binary register and written to the raw data file; see displaying and downloading your results. The histogram will show the normalized frequency of each state of the binary register.

Qubit initialization and measurement

On our hardware backends all qubits will always be initialized in the ground state at the beginning of each shot and all qubits will always be measured at the end of each shot, even when the user does not supply a prep statement at the begin or a measure statement at the end of the algorithm. The measure statement at the end of an algorithm merely determines which measurement results are returned to the user. The following situations must be considered:

  1. The measure_all statement is included at the end of the algorithm

In this case all measured output states are returned.

  1. No measure (or measure_all, measure_x etc) statement is included at the end of an algorithm

In this case the system will return all measured states to the user (because it does not make sense to return no results to the user). This is therefore equivalent to a measure_all statement.

  1. A measure, measure_x, measure_y or measure_z is included but not for all qubits (e.g. only for qubit 0)

In this case binning is done which means that only the measurement probabilities for the measured qubit are returned, irrespective of the results of the non-measured qubit (for which the output probability is then set to zero).

Note: algorithms for hardware backends must always include a qubits 2 command (for Spin-2) or qubits 5 command (for Starmon-5) in the cQASM file.

Number of operations

The number of quantum operations that return a meaningful result is mainly determined by the coherence times (T1 and T2*) of the qubits which determines to a large extend the operational fidelities. The actual gate count is also determined by the decomposition of the gates. As an example, a SWAP gate on Spin-2 will be decomposed into 3 CZ gates and some single-qubit gates. Furthermore, the individual backends will limit the number of operations that can be executed. If you try to execute too many operations in one shot, the system will return an error and your job will not be executed.

Number of shots

Our hardware backends allow you to do a large number of shots to determine the output probabilities of the individual states. The maximum number of shots is limited by the memory capabilities of the data acquisition hardware that is used and is given in the accounts overview.