Implementing the Quantum von Neumann Architecture with Superconducting Circuits

Abstract

The von Neumann architecture for a classical computer comprises a central processing unit and a memory holding instructions and data. We demonstrate a quantum central processing unit that exchanges data with a quantum random-access memory integrated on a chip, with instructions stored on a classical computer. We test our quantum machine by executing codes that involve seven quantum elements: Two superconducting qubits coupled through a quantum bus, two quantum memories, and two zeroing registers. Two vital algorithms for quantum computing are demonstrated, the quantum Fourier transform, with 66% process fidelity, and the three-qubit Toffoli-class OR phase gate, with 98% phase fidelity. Our results, in combination especially with longer qubit coherence, illustrate a potentially viable approach to factoring numbers and implementing simple quantum error correction codes.

Superconducting quantum circuits at the surface code threshold for fault tolerance

“…The two-qubit CZ gate is implemented by tuning one qubit in frequency along a "fast adiabatic" trajectory which takes the two-qubit |11 state close to the avoided-level crossing with the |02 state, yielding a state-dependent relative phase shift. This implementation is the natural choice for weakly anharmonic, frequency-tunable qubits, as the other computational states are left unchanged 8,22,23 . Having the CZ gate adiabatic as well as fast is advantageous.…”

Computing prime factors with a Josephson phase qubit quantum processor

“…Compiled versions of Shor's algorithm have been demonstrated on ensemble quantum systems [2] and photonic systems [3][4][5], however this has yet to be shown using solid state quantum bits (qubits). Two advantages of superconducting qubit architectures are the use of conventional microfabrication techniques, which allow straightforward scaling to large numbers of qubits, and a toolkit of circuit elements that can be used to engineer a variety of qubit types and interactions [6,7]. Using a number of recent qubit control and hardware advances [7][8][9][10][11][12][13], here we demonstrate a nine-quantum-element solid-state QuP and show three experiments to highlight its capabilities.…”

“…Two advantages of superconducting qubit architectures are the use of conventional microfabrication techniques, which allow straightforward scaling to large numbers of qubits, and a toolkit of circuit elements that can be used to engineer a variety of qubit types and interactions [6,7]. Using a number of recent qubit control and hardware advances [7][8][9][10][11][12][13], here we demonstrate a nine-quantum-element solid-state QuP and show three experiments to highlight its capabilities. We begin by characterizing the device with spectroscopy.…”

“…In the final experiment, we run a three-qubit compiled version of Shor's algorithm to factor the number 15, and successfully find the prime factors 48 % of the time. Improvements in the superconducting qubit coherence times and more complex circuits should provide the resources necessary to factor larger composite numbers and run more intricate quantum algorithms.In this experiment, we scaled-up from an architecture initially implemented with two qubits and three resonators [7] to a nine-element quantum processor (QuP) capable of realizing rapid entanglement and a compiled version of Shor's algorithm. The device is composed of four phase qubits and five superconducting coplanar waveguide (CPW) resonators, where the resonators are used as qubits by accessing only the two lowest levels.…”

Quantum-circuit refrigerator

“…If demonstrated in a superconducting qubit, these numbers would represent a clear improvement in the present state-of-the-art initialization schemes [14][15][16][17][18][19][20] . Interestingly, Fig.…”