Figure: Experimental setup.
Quantum memory that relies on quantum band integration is a key component in developing quantum networks that are compatible with fiber optic communication infrastructure. Quantum engineers and information technology experts have yet to create such a high-capacity network that can form integrated multimode photonic quantum memories in communication frequency bands.
In a new report in Science Advances, Xueying Zhang and a team of researchers describe optical fiber integrated multimode storage of single photons in the communication band on a laser direct writing chip.
A memory device made of fiber pigtail erbium-doped (Er3+) lithium niobate (Er3+:LiNbO3) provides a memory system that is integrated with an on-chip component of a telecom band fiber integrated. The results of this study highlight the potential for the formation of future quantum networks based on integrated photonics devices.
Photon quantum memory
Quantum states of light can be reversibly mapped onto matter to create photonic quantum memory, ideal for long-distance quantum communication across distributed quantum networks.
Physicists have integrated photonic quantum storage devices based on optical waveguides with other integrated quantum devices, such as quantum light sources, photonic circuits, and single-photon detectors, to design interconnected multifunctional quantum architectures. In this work, Zhang et al. developed an integrated multimode memory device for telecommunication bands based on lithium niobate waveguides.
The laser writing waveguide they designed uses femtosecond laser micromachining to directly couple to a single-mode fiber pigtail, by using optical collimators on both sides of the device to promote compatibility with fiber optic communication systems.
The team developed an on-chip quantum memory system that uses an atomic frequency comb protocol. The integration of a 4 ghz wide atomic frequency comb enabled the team to experimentally implement a multi-mode quantum memory system, paving the way for the formation of an integrated quantum network with memory compatible with fiber optic communication infrastructure.
Figure: Fabrication and calibration of Er3+ : LiNbO3 waveguide.
experiment
Zhang et al. used femtosecond laser micromachining technology to fabricate type III waveguides on erbium-doped lithium niobate crystal wafers and designed a memory device.
The bulk crystals of the material maintain the concentration of doped ions to an extremely small percentage and allow the laser to write the coupling between the waveguide and the single-mode fiber. The scientists glued doped lithium niobate crystals to a copper radiator with an optical collimator with two single-mode fiber braids.
They placed the fiber-optic integration unit in a dilution refrigerator and observed a total optical transmission frequency of 26 percent for the entire cryogenic unit.
Multimode storage
Multimode storage experiments include generating single photons and preparing quantum storage and measurement systems based on atomic frequency combs. The team generated the correlated photon pairs through a cascade of second harmonic generation and spontaneous parameter down-conversion processes in a lithium niobate waveguide module pumped with a series of light pulses.
For single-mode storage, the team used a single laser pulse with a duration of 300 picoseconds. The scientists detected photons in the device with a superconducting nanowire single-photon detector. Zhang et al. analyzed the instrument's detection signals using a time-to-digital converter.
Zhang and his colleagues delivered Erbium (Er3+) ions into a periodic absorption structure, such as an atomic frequency comb with a tooth spacing of 5 MHz, which corresponds to a storage time of 200 nanoseconds. The team demonstrated the storage of non-classical light with a large time-bandwidth product.
They then sent the signal photons to the atomic frequency comb memory and calculated the efficiency of the system. Based on the transmission efficiency of the storage device and the spectral filtering of the input photons, they calculated the internal storage efficiency. The results show that the quantum memory of the atomic frequency comb preserves the single photon purity and spectral purity.
These results allowed Zhang et al. to build an on-chip quantum memory with a memory time of 200 nanoseconds, while establishing negligible crosstalk in the instrument.
foreground
In this way, an integrated multimode quantum memory based on laser writing erbium-doped lithium niobate waveguide is demonstrated. The team achieved a storage bandwidth of 4 GHz and a storage time of 200 nanoseconds.
These achievements in wideband multimode quantum storage will open the way for the generation of high-rate quantum networks. While these results are important, the researchers believe that several upgrades are still needed to design a fully functional device to facilitate quantum networks.
The current approach integrates the reliability of fiber integrated devices compatible with fiber telecommunications infrastructure to provide promising laser writing components with wideband multiplexed storage characteristics. The research team hopes to combine a photon pair source with an integrated memory to implement a high-rate quantum repeater protocol, thereby creating a large-scale quantum network.
These results will contribute to the realization of quantum systems with large capacity, scalability, and compatibility for fiber optic communication, with implications for the future and the construction of global quantum networks.
Source: Chinese Optical Journal Network
