Benchmarking gate-based quantum computers

With the advent of public access to small gate-based quantum processors, it becomes necessary to develop a benchmarking methodology such that independent researchers can validate the operation of these processors. We explore the usefulness of a number of simple quantum circuits as benchmarks for gate-based quantum computing devices and show that circuits performing identity operations are very simple, scalable and sensitive to gate errors and are therefore very well suited for this task. We illustrate the procedure by presenting benchmark results for the IBM Quantum Experience, a cloud-based platform for gate-based quantum computing.Comment: Accepted for publication in Computer Physics Communication

Massively parallel quantum computer simulator, eleven years later

A revised version of the massively parallel simulator of a universal quantum computer, described in this journal eleven years ago, is used to benchmark various gate-based quantum algorithms on some of the most powerful supercomputers that exist today. Adaptive encoding of the wave function reduces the memory requirement by a factor of eight, making it possible to simulate universal quantum computers with up to 48 qubits on the Sunway TaihuLight and on the K computer. The simulator exhibits close-to-ideal weak-scaling behavior on the Sunway TaihuLight,on the K computer, on an IBM Blue Gene/Q, and on Intel Xeon based clusters, implying that the combination of parallelization and hardware can track the exponential scaling due to the increasing number of qubits. Results of executing simple quantum circuits and Shor's factorization algorithm on quantum computers containing up to 48 qubits are presented.Comment: Substantially rewritten + new data. Published in Computer Physics Communicatio

Superconducting flux qubits compared to ideal two-level systems as building blocks for quantum annealers

For quantum computers, two theoretical models are nowadays considered to be the most important: the gate-based quantum computer and the quantum annealer.Gate-based quantum computers are based on computational gates just like classical computers, but have potentially more computational power due to the algebra behind quantum theory. A quantum annealer works fundamentally different: First the system is prepared in a known ground state of an initial Hamiltonian, then this Hamiltonian is adiabatically transformed into the final Hamiltonian whose ground state corresponds to the solution of a given problem, usually taken from the class of optimization problems.Quantum annealing works well in theory if the qubits can be modeled as two-level systems. However, in real devices, the qubits are not based on perfect two-level systems, but on a two-dimensional subspace of a larger system. This makes approximations in analytic calculations unavoidable.With a simulation utilizing the Suzuki-Trotter product-formula approach to solve the time-dependent Schrödinger equation, the time-evolution of the full state of such a device based onsuperconducting flux qubits is investigated

Simulation of gate-based quantum computers with superconducting qubits

Over the last decades, tremendous effort has gone into building a universal quantum computer. In theory, such a device can solve certain problems such as factoring exponentially faster than digital computers. The leading technological prototypes are based on superconducting circuits and comprise up to 17 qubits. Controlling these fragile systems requires an enormous amount of precision, posing a difficult challenge for the experimentalists. We study such quantum systems in detail by solving the time-dependent Schrödinger equation for a generic model Hamiltonian. For this purpose, we have developed efficient product-formula algorithms that are tailored to key features of the model Hamiltonian. This allows us to simulate every individual controlling pulse that is used in experiments to realize a certain quantum gate, as dictated by the computational model of a quantum computer. By optimizing the pulse parameters, we find that even in the ideal case, the best pulses still contain undesirable errors in the realization of the intended quantum gate. The common gate metrics measured and reported in experiments or computed in theory are shown to provide insufficient practical information about the significance of these errors

Simulation of a Quantum Annealer Based on Superconducting Flux Qubits

For quantum computers, there are two theoretical models which are nowadays considered to be the most important: the gate-based quantum computer and the quantum annealer.Gate-based quantum computers are based on computational gates just like classical computers are, but have potentially more computational power due to the algebra behind quantum theory. A quantum annealer works fundamentally different: First the system is prepared in a known ground state of an initial Hamiltonian, then this Hamiltonian is adiabatically transformed into the final Hamiltonian whose ground state corresponds to the solution of a given problem, usually taken from the class of optimization problems.Quantum annealing works well in theory if the qubits can be described by two-level systems. However, in real devices qubits are not based on a perfect two-level system, but on a two-dimensional subspace of a larger system. This makes approximations in analytic calculations unavoidable.With a simulation utilizing the Suzuki-Trotter product-formula approach for solving the time-dependent Schrödinger equation, the time-evolution of the full state of such a device based on superconducting flux qubits is investigated

Error analysis of gate-based quantum computers with transmon qubits

Over the past decades, tremendous effort has gone into building a universal quantum computer. In theory, such a device can solve certain problems such as factoring exponentially faster than digital computers. The leading technological prototypes are based on superconducting circuits and contain about 10-50 qubits. Controlling these fragile systems requires an enormous amount of precision, posing a difficult challenge for the experimentalists. We study such quantum systems in detail by solving the time-dependent Schrödinger equation for a generic model Hamiltonian. For this purpose, we have developed efficient product-formula algorithms that are tailored to key features of the model Hamiltonian. This allows us to simulate each individual voltage pulse that is used in experiments to realize a certain quantum gate, as dictated by the computational model of a quantum computer. By optimizing the pulse parameters, we find that even in the ideal case, the best pulses still contain undesirable errors in the realization of the intended quantum gate. The common gate metrics measured and reported in experiments or computed in theory are shown to provide insufficient practical information about the significance of these errors

Benchmarking gate-based quantum computers

With the advent of public access to small gate-based quantum processors, it becomes necessary to develop a benchmarking methodology such that independent researchers can validate the operation of these processors. We explore the usefulness of a number of simple quantum circuits as benchmarks for gate based quantum computing devices and show that circuits performing identity operations are very simple, scalable and sensitive to gate errors and are therefore very well suited for this task. We illustrate the procedure by presenting benchmark results for the IBM Quantum Experience, a cloud-based platform for gate-based quantum computing. (C) 2017 The Author(s). Published by Elsevier B.V