The University of Basel has achieved a significant milestone in quantum technology by constructing a quantum memory element utilizing atoms confined within a minute glass cell. This breakthrough opens the door to a future where quantum memories could be produced on a mass scale, potentially on a wafer.
In envisioning a world driven by quantum technologies, analogous to our dependence on the internet and mobile phone networks today, the researchers at Basel are paving the way for quantum networks. These networks are anticipated to facilitate secure message transmission through quantum cryptography and establish connections between quantum computers.
Much like conventional networks, these quantum networks necessitate memory elements capable of temporarily storing and directing information as required. Professor Philipp Treutlein and his team at the University of Basel have successfully engineered such a memory element, notable for its micro-fabrication capabilities, rendering it suitable for large-scale production. Their groundbreaking findings have been documented in Physical Review Letters.
Photon storage in glass cells
Harnessing the unique attributes of light particles, researchers have identified photons as ideal carriers for transmitting quantum information. These photons can traverse fiber optic cables, reach satellites, or be directed into a quantum memory element. In this memory element, the quantum state of photons must be precisely stored and later converted back into photons after a designated duration.
Two years ago, the University of Basel researchers demonstrated the effectiveness of this process using rubidium atoms within a handmade glass cell several centimeters in size. However, for practical everyday use, the challenge was to shrink these cells and enable mass production. Postdoc Dr. Roberto Mottola explains the need for smaller cells: “To be suitable for everyday use, such cells need to be smaller and amenable to being produced in large numbers.”
Now, Professor Philipp Treutlein and his team have achieved precisely that. By utilizing a few-millimeter-sized cell obtained from the mass production of atomic clocks, they overcame the challenges. To maintain an adequate number of rubidium atoms for quantum storage in the smaller cell, they employed a strategy of heating the cell to 100°C to increase vapor pressure.
In a further ingenious move, the researchers exposed the atoms to a magnetic field 10,000 times stronger than Earth's magnetic field—1 tesla. This manipulation of atomic energy levels facilitated quantum storage of photons, assisted by an additional laser beam. With this method, the researchers successfully stored photons for approximately 100 nanoseconds, a time during which free photons would have traveled 30 meters.
A 1,000 quantum memories on a single wafer
Professor Philipp Treutlein highlights a groundbreaking achievement, stating, “For the first time, we have constructed a miniature quantum memory for photons, allowing the simultaneous production of approximately 1,000 copies on a single wafer.”
In the recent experiment, storage capabilities were showcased using strongly attenuated laser pulses. Looking ahead, Treutlein, in collaboration with CSEM in Neuchatel, aims to advance the technology to store single photons within these miniature cells. Additionally, the optimization of the glass cell format is on the agenda to maximize the duration of photon storage while maintaining their delicate quantum states.
Source: University of Basel