Research of digital qubites for heterogeneous digital quantum coprocessors

Abstract

Recently, interest is growing towards real quantum computers, which are analog and probabilistic devices by nature. The
interest is also growing to their digital version, both software and hardware. One approach to the construction of real quantum
computers is to use quantum chips. The hardware implementation of digital quantum computers involves the use of field
programmable gate arrays. A digital quantum coprocessor has already been created which has over a thousand digital qubits and can
perform such complex algorithms as a quantum Fourier transformation. The created and working digital quantum coprocessor can
already be used to work out various quantum algorithms, algorithms for the interaction of a classic computer and its quantum
coprocessor, as well as for research various options for building digital qubits. The purpose of this work is to study the effect of the
accuracy of the presentation of the state of digital qubit on the probability of obtaining the correct results of the digital quantum
coprocessor. For the study, a heterogeneous digital quantum coprocessor with thirty two digital qubits is selected, which will
perform the Fourier quantum transformation. The article describes the basics of building digital quantum coprocessors. Schemes that
illustrate the interaction of a classic computer and a quantum coprocessor, the architecture of the coprocessor and the possible
structures of its digital qubits are given. Two variants of the coprocessor, homogeneous one with one pseudo-random codes generator
and one comparator, and heterogeneous one, with a generator and a comparator in each digital quantum cell, from which digital
qubits consist, are shown. Two options for comparators are also shown - with a direct functional converter and with reverse one. In
this work, the influence of the length of the qubit state codes of heterogeneous digital quantum coprocessors on the probability of the
correct results formation is investigated. It was shown that the probability of obtaining the correct results at the output of the digital
heterogeneous coprocessor is sharply (up to fifty percent) improved with a decrease of the qubit state code length, that is, with a
decrease in the coprocessor hardware cost. With a length of a code equal to two bits, the quality of the operation of the heterogeneous
coprocessor becomes commensurate with the quality of the homogeneous one. The need for additional research in this direction,
including with homogeneous coprocessors, is shown.