Cryogenic-DRAM based memory system for scalable quantum computers

Abstract

A quantum computer can solve fundamentally difficult problems by utilizing properties of quantum bits (qubits). It consists of a quantum substrate, connected to a conventional computer, termed as control processor. A control processor can manipulate and measure the state of the qubits and act as an interface between qubits and the programmer. Unfortunately, qubits are extremely noise-sensitive, and to minimize the noise; qubits are operated at cryogenic temperatures. To build a scalable quantum computer, a control processor which can work at cryogenic temperatures is essential [3, 14]. In this paper, we focus on the challenges of building a memory system for a cryogenic control processor. A scalable quantum computer will require large memory capacity for storing the program and the data generated by the quantum error correction. To this end, we evaluate the feasibility of cryogenic DRAM-based memory system by characterizing commercial DRAM modules at cryogenic temperatures. In this paper, we report the minimum operational temperature for 55 DIMMs (consisting of a total of 750 DRAM chips) and analyze the error patterns in commodity DRAM devices operated at cryogenic temperatures. Our study shows that a significant fraction of DRAM chips continue to work at temperatures as low as 80K. This study is an initial step towards evaluating the effectiveness of cryogenic DRAM as a main memory for quantum computers.