Newswise \u2014 Researchers have touted the revolutionary potential of quantum computers to take on otherwise intractable challenges, like modeling complex molecular behavior for drug discovery or factoring enormous numbers in use for cryptography schemes. But what would a large-scale quantum computer actually look like?<\/p>\n
That turns out to be a difficult question to answer, even in general terms. Add parameters and specifications and it becomes even more daunting.<\/p>\n
But with help from the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, the Defense Advanced Research Projects Agency (DARPA) is attempting to do just that: define, in practical terms, what a useful quantum computer looks like and how it must be built.<\/p>\n
Announced in 2022<\/a>, DARPA\u2019s Underexplored Systems for Utility-Scale Quantum Computing (US2QC) program aims to evaluate less-taken roads to determine whether quantum computing at scale might be achieved in a matter of years rather than decades, as many experts predict \u2014 and if so, how. In July 2024, DARPA announced<\/a> that US2QC will be combined with a related program to found the Quantum Benchmarking Initiative (QBI), which builds and expands upon US2QC.<\/p>\n Joan Hoffmann<\/a>, who leads the Research and Exploratory Development Mission Area<\/a> at APL, expressed excitement at the Laboratory\u2019s role in this effort.<\/p>\n \u201cThe earliest computers were massive mechanical calculators, and then from there the field went to using vacuum tubes, but what ultimately pushed computers forward was the discovery of transistors,\u201d Hoffmann said. \u201cNo one knows what the equivalent of the transistor will be for quantum computing, but it\u2019s fascinating to dig in and try to figure that out.\u201d<\/p>\n More Qubits, Fewer Errors<\/p>\n The beating heart of quantum computing is the quantum bit, or qubit. Unlike classical computer bits, which are coded as either zeros or ones, qubits can exist in multiple states at once. The combination of a qubit\u2019s analog nature \u2014 its ability to take values other than exactly zero or one \u2014 and entanglement, which connects multiple qubits in nonintuitive ways, allows for novel and extremely efficient solutions for certain challenging problems.<\/p>\n But these very properties also make qubits extremely sensitive to their environment, and thus error-prone.<\/p>\n The quest for a utility-scale quantum computer can be summarized in four deceptively simple words: more qubits, fewer errors. Accuracy demands two more: millions more qubits, far fewer errors.<\/p>\n Therein lies the rub.<\/p>\n \u201cThe two current leading technologies \u2014 superconducting qubits and ion traps \u2014 have shown incredible performance at the single qubit level, but it\u2019s not known whether their dominance will continue as larger fault-tolerant algorithm-scale designs become the focus of the field,\u201d said Scott Hendrickson<\/a>, APL\u2019s US2QC project manager. \u201cThere are many hard problems that have to be solved in order to scale these technologies toward millions of qubits.\u201d<\/p>\n The solution, ironically, may come from technologies that academics threw out long ago, such as photonics, topological quantum computing and trapped neutral atoms: approaches that were slow to mature for making systems with small numbers of qubits, Hendrickson says, but may turn out to be much better for creating systems with millions of them. And commercial companies are now picking up on that advantage.<\/p>\n In January 2023, DARPA selected three companies<\/a> and tasked them with presenting a design concept for a utility-scale quantum computer. In February, after almost two years of rigorous technical analysis of the design concepts, two of those companies were selected<\/a> to advance to the program\u2019s validation and co-design phase; and in April, the agency announced<\/a> that nearly 20 quantum computing companies have been chosen to participate in the initial stage of QBI, in which they will characterize their unique concepts for creating a useful, fault-tolerant quantum computer within a decade.<\/p>\n Engineering Not-Yet-Existent Systems<\/p>\n