University of Science and Technology of China prepares high-performance integrated solid-state quantum memory

[ Instrument Network Instrument R & D ] Guo Guangcan, an academician of the Chinese Academy of Sciences and a professor at the University of Science and Technology of China, has made new progress in the field of quantum storage. The team Li Chuanfeng, Zhou Zongquan and others used femtosecond laser micromachining technology to prepare high-fidelity integratable solid-state quantum memories, and based on the self-developed equipment, for the first time, the electronic spin and nuclear spin coherence life of the rare earth ions were fully improved.

Electron spin is one of the basic properties of electrons. Abbreviation for quantum number of electron intrinsic motion or electron intrinsic motion. In 1925, GE Uhlenbeck and SA Guzmit were inspired by Pauli's incompatibility principle, analyzed some experimental results of atomic spectrum, and proposed that electrons have intrinsic motion—spin, and that they are related to electron spin. Spin magnetic moment. This can explain the fine structure of the atomic spectrum and the anomalous Zeeman effect. The spin angular momentum of the electron is shown in the figure, where the electron spin S = 1/2. In 1928, PAM Dirac proposed the electron's relativistic wave equation. The equation naturally includes the electron spin and the spin magnetic moment. Electron spin is a quantum effect and cannot be understood classically. If electron spin is viewed as a rotation around an axis, a contradictory result is obtained.

Quantum memory is the core device for constructing a quantum network. It can effectively overcome the channel loss and thereby extend the working distance of quantum communication. It can also integrate quantum computing and quantum sensing resources in different places. The current research on solid-state quantum memory faces two challenges. On the one hand, the storage media used in the existing solid-state quantum storage experiments are mostly block crystals. This kind of material cannot directly connect to optical fiber networks or integrate optical chips, which is difficult to achieve large-scale scalability. application.

On the other hand, the electronic spins and nuclear spins of rare earth ions interact with phonons in the crystal, causing the coherence life of the quantum memory to be severely limited. In order to promote the practical application of quantum memory, the research group began a systematic study of the above issues from material processing and testing equipment. Rare earth is a general term for lanthanides, thorium and yttrium, seventeen metal elements in the chemical periodic table. There are 250 rare earth ores in nature. The earliest discovered rare earth was Finnish chemist John Gadolin. In 1794, he separated the first rare earth "element" (yttrium earth, Y2O3) from a piece of heavy ore shaped like asphalt. Because there were fewer rare earth minerals discovered in the 18th century, only a small amount of water-insoluble oxides could be made by chemical methods at that time. This oxide has been habitually called "earth" in history, hence the name rare earth.

In order to solve the problem of scalability, the research group used femtosecond laser micromachining technology to etch an optical waveguide in an erbium-doped yttrium silicate crystal for the first time, and developed an integrated solid-state quantum memory. The waveguide area is 150 microns from the crystal surface and the waveguide width is 20 microns. It can be integrated with other micro-nano electronics and micro-nano optics. Due to the high power density of the light field in the waveguide region, the control laser power required for the experiment was reduced by about 30 times compared to the power required for the bulk crystal. In the experiment, two kinds of optical quantum storage schemes of atomic frequency comb (AFC) and low noise echo recovery (ROSE) were demonstrated, and the storage fidelity was measured through the interference between the reference optical signal and the memory readout optical signal. The fidelity corresponding to the two schemes exceeds 99% and 97%, respectively, indicating that this integrated quantum memory has high reliability.

An effective solution to the problem of limited coherence life is to construct a pulsed electron and nuclear spin dual resonance spectrometer (ENDOR) at deep low temperature (<0.5K), thereby reducing phonons and polarizing electron spins. Due to the high thermal load in a traditional commercial ENDO system, its operating temperature cannot generally be lower than 4K. Previously, the international academic community generally believed that deep low temperature ENDO was an unattainable task. After solving a series of technical problems, the research team successfully built a deep low-temperature pulsed electron and nuclear spin dual resonance spectrometer, and strictly calibrated its minimum operating temperature to 0.1K. At 0.1K, the measured signal-to-noise ratio of the spin echo signal of the Nd-doped yttrium silicate was 20 times higher than that at 4K, and the population life and coherence life of the electron spin reached 15 seconds and 2 respectively. At the same time, the population life and coherence life of nuclear spins reach 10 minutes and 40 ms, respectively. These four life indicators have achieved an order of magnitude improvement over 4K temperature.

Optica reviewers commented: "This work is very important. It demonstrates the diversity of experimental techniques and solutions and proves that the optical waveguide etched in rare earth-doped crystals is a very promising platform in the field of quantum information."

Physical Review Applied reviewers commented: "These measurements are based on an mK-class temperature ENDO spectrometer developed by the author. This is a rare international device ... this device enables some physical systems to achieve more accurate spectra Analysis, entered a temperature range that was difficult to reach before. "" From 4K to 100mK, the coherence life of electron spins and nuclear spins has been increased by more than an order of magnitude. This is the first time that deep-temperature observations have been made of rare earth ions. Significantly enhanced spin coherence life. "

Source: University of Science and Technology of China, Encyclopedia