Experimental comparison of two quantum computing architectures

Abstract

We run a selection of algorithms on two state-of-the-art 5-qubit quantum computers that are based on different technology platforms. One is a publicly accessible superconducting transmon device (www.research.ibm.com/ibm-q) with limited connectivity, and the other is a fully connected trapped-ion system. Even though the two systems have different native quantum interactions, both can be programed in a way that is blind to the underlying hardware, thus allowing a comparison of identical quantum algorithms between different physical systems. We show that quantum algorithms and circuits that use more connectivity clearly benefit from a better-connected system of qubits. Although the quantum systems here are not yet large enough to eclipse classical computers, this experiment exposes critical factors of scaling quantum computers, such as qubit connectivity and gate expressivity. In addition, the results suggest that codesigning particular quantum applications with the hardware itself will be paramount in successfully using quantum computers in the future.quantum computing | quantum information | quantum information science | quantum physics | quantum computing architecture I nspired by the vast computing power a universal quantum computer could offer, several candidate systems are being explored. They have allowed experimental demonstrations of quantum gates, operations, and algorithms of ever-increasing sophistication. Recently, two architectures, superconducting transmon qubits (1-5) and trapped ions (6, 7), have reached a new level of maturity. They have become fully programmable multiqubit machines that provide the user with the flexibility to implement arbitrary quantum circuits from a high-level interface. This makes it possible for the first time to test quantum computers irrespective of their particular physical implementation.Whereas the quantum computers considered here are still small scale and their capabilities do not currently reach beyond small demonstration algorithms, this line of inquiry can still provide useful insights into the performance of existing systems and the role of architecture in quantum computer design. These will be crucial for the realization of more advanced future incarnations of the present technologies.The standard abstract model of quantum computation assumes that interactions between arbitrary pairs of qubits are available. However, physical architectures will in general have certain constraints on qubit connectivity, such as nearest-neighbor couplings only. These restrictions do not in principle limit the ability to perform arbitrary computations, because swap operations may be used to effect gates between arbitrary qubits using the connections available. For a general circuit, reducing a fully connected system to the more sparse star-shaped or linear nearestneighbor connectivity requires an increase in the number of gates of O(n), where n is the number of qubits (8). How much overhead is incurred in practice depends on the connections used in a particular circuit and how effi...

Quantum Computers as Universal Quantum Simulators: State‐of‐the‐Art and Perspectives

“…As a general comment, trapped ions quantum simulators allow deeper quantum circuits with better performance, that is, a larger number of Trotter steps is possible. This is in line with recent studies comparing the two platforms when challenged with similar quantum algorithms on 5 qubits processors . One may notice that 5 Trotter steps are currently a limiting value for superconducting circuit quantum simulators, where the fidelity drops to values slightly above 60%, still far from an acceptable result, also in view of scalability.…”

“…On the other hand, a quantum processor based on 11 hyperfine qubits has recently been shown to achieve an all‐to‐all connectivity with single‐ and two‐qubit XX gate fidelities of 99.5% and 97.5% on average, respectively . It is interesting to notice that these results improve previous reports on an analogous 5‐qubits quantum processor, as a clear signature of the ongoing development. At time of writing, we are not aware of any digital quantum simulation of spin models performed on quantum processors based on hyperfine qubits, although it would be interesting to test them with some of the algorithms presented in this Review.…”

Demonstration of the Quantum No-Hiding Theorem in a Category Theoretic Framework: An IBM Quantum Experience

“…It is world's first commercial quantum computing service provided by IBM, and permits a user to run quantum algorithms via the IBM cloud and implement quantum circuits. Using this web interface researchers have run a variety of quantum computing experiments and demonstrations, e.g., [2][3][4][5][6][7][8][9][10][11].…”

External current as a coupler between the spin-vortex-induced loop current qubits

“…(2) The operation temperature may be too low. The operation temperature for the superconducting qubit is in the order of mK [4]. Maintaining a large number of qubits intact with keeping such low temperature may be too difficult and too expensive [5].…”