Physicists set new record for quantum memory efficiency

Like memory in conventional computers, quantum memory components are essential for quantum computers – a new generation of data processors that exploit quantum mechanics and can overcome the limitations of conventional computers. With their powerful computing power, quantum computers can push the boundaries of basic science to create new drugs, explain cosmological mysteries, or improve the accuracy of predictions and optimization plans. Quantum computers should be much faster and more powerful than their traditional counterparts because the information is computed in bits, which, unlike the bits used in conventional computers, can represent both zero and one in a simultaneous super-state.

The photonic quantum memory allows the storage and recovery of quantum states flying to a photon. However, the production of this highly efficient quantum memory remains a major challenge because it requires a perfectly adapted photon-material quantum interface. Meanwhile, the energy of a single photon is too low and can easily be lost in the noisy sea from the background parasite. For a long time, these problems have reduced the efficiency of quantum memory to less than 50% – a crucial threshold value for practical applications.

For the first time now, a joint research team led by Professor Du Shengwang of HKUST, SCNU Professor Zhang Shanchao, UNSC Professor Yan Hui and UNSC Professor Zhu Shi-Liang and the University of Nanjing has found a way to increase the efficiency of quantum photonic memory to over 85% with over 99% fidelity.

The team created such a quantum memory by trapping billions of rubidium atoms in a tiny space resembling a hair. These atoms are cooled to near absolute zero (about 0.00001 K) using lasers and a magnetic field. The team also found a clever way to distinguish a photon from the noisy background light. This discovery brings the dream of a universal quantum computer closer to reality. Such quantum memory devices can also be deployed as repeaters in a quantum array, thus laying the foundation for a new generation of the quantum internet.

"In this work, we are coding a flying qubit on the polarization of a single photon and storing it in laser-cooled atoms," said Professor Du. "Although the quantum memory demonstrated in this work concerns only one qubit operation, it paves the way for future quantum technology and quantum engineering."

The discovery was recently published as a cover of the authoritative journal Photonic Nature, the latest in a series of research from Professor Du's lab on Quantum Memory, begun in 2011.