This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Classical computers can temporarily store the information required to perform specific tasks in a short-term memory component known as RAM (random access memory). This component allows computer processors to retrieve information from a chosen location without searching through all stored data.
Yet most current superconductor-based quantum computers do not have a separate RAM-like component. This is because while processors and memory components are separate in classical computers, most superconducting quantum computers rely on the same hardware for storing and processing information. Researchers at Stanford University, University of Chicago, the SLAC National Accelerator Laboratory and other institutions have designed a new device that could serve as a random access quantum memory.
Their device, presented in a paper published in Nature Physics, could pave the way for quantum computers with separate memory components and fewer signal-carrying connections. "In quantum computers, every qubit is a processor bit, and each one needs its own microwave electronics and wiring running down into a refrigerator that is already crowded," David I. Schuster, senior author of the paper, told Phys.org.
"If every additional qubit costs another set of control hardware, scaling stops being a physics problem and becomes an engineering one." To provide superconductor-based quantum computers with compact memory components, Schuster and his colleagues have long been trying to develop microwave cavities that support many modes at once. In this context, modes are distinct patterns in which microwave energy can oscillate inside a cavity, and each mode could serve as a separate data storage site. "Think of a metal box in which many separate notes can ring at the same time, each able to hold a qubit's worth of information, and each able to hold it for a long time," explained Schuster.
"The obvious thought is to use each note to represent a different qubit of memory. The obstacle has always been control: to write to them you have to connect them to a superconducting qubit called a transmon, and a transmon creates interactions between objects it connects. That is exactly what makes it good at computing, and exactly what disturbs the delicate states you are trying to store." To resolve this long-standing challenge, the researchers proposed introducing a buffer between a quantum processor and a memory, instead of connecting them directly.
The device they designed has four key components: a transmon, a multimode aluminum cavity, a buffer cavity and a tunable coupler for transferring quantum states between the buffer and a chosen memory cell. "The transmon does the computing, the multimode aluminum cavity has seven modes that act as individually addressable memory cells, and the buffer cavity between them works rather like a cache, or a workbench," explained Schuster. "Choosing a memory cell is much like tuning a radio to a station.
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