Quantum frequency conversion, important for a worldwide quantum Internet, is being advanced by the HiFi project, which deals with wavelength inequalities and supports quantum communications. Credit: SciTechDaily.comFraunhofer IAF achieves record output power with VECSEL for quantum frequency converters.The expansion of fiber optics is advancing worldwide, which not only increases the bandwidth of standard Internet connections, but also brings closer the awareness of an international quantum Internet. The quantum web can help to fully exploit the capacity of specific technologies. These include much more powerful quantum computing through the connecting of quantum processors and registers, more secure interaction through quantum key distribution or more accurate time measurements through the synchronization of atomic clocks.However, the distinctions in between the glass fiber requirement of 1550 nm and the system wavelengths of the various quantum bits (qubits) realized to date represent a hurdle, because those qubits are mostly in the noticeable or near-infrared spectral variety. Researchers wish to overcome this obstacle with the help of quantum frequency conversion, which can particularly change the frequencies of photons while keeping all other quantum properties. This allows conversion to the 1550 nm telecom variety for low-loss, long-range transmission of quantum states.VECSEL setup for the development of a low-noise pump source for quantum frequency conversion. Credit: © Fraunhofer IAFProject HiFi: Enabling technologies for quantum frequency conversionIn the joint project “HiFi– Highly integrated quantum frequency converter of greatest fidelity based upon ingenious laser, fiber and production technology” moneyed by the German Federal Ministry of Education and Research (BMBF), scientists are dealing with the realization of all essential technologies to supply quantum frequency converters (QFK) with high efficiency and low sound for initial test tracks. The Fraunhofer Institute for Applied Solid State Physics IAF has actually added to the project with the successful development of disk lasers (also called vertical-external-cavity surface-emitting lasers, VECSELs) based on gallium antimonide (GaSb). These are optically pumped, surface-emitting semiconductor lasers with an external resonator and intracavity filter for wavelength selection.Single-mode VECSEL module with up to 2.4 W output power for the frequency variety between 1.9 and 2.5 µm, established as a pump source for quantum frequency converters. Credit: © Fraunhofer IAF2.4 W output power with outright frequency stability below 100 kHz”The VECSELs we established as part of HiFi are spectrally narrow-band pump sources which, depending on the output wavelength of the qubits utilized, specifically cover a wavelength in between 1.9 and 2.5 µm and attain an output power of as much as 2.4 W with an absolute wavelength stability of less than 2 fm. This corresponds to a frequency stability of less than 100 kHz and clearly falls below the frequency stability class 1E-9. The outcome represents an international record for this type of laser,” describes Dr. Marcel Rattunde, HiFi sub-project organizer and head of the optoelectronics department at Fraunhofer IAF.”The outcome was enabled by the close cooperation with project partner MENLO Systems GmbH. Together, we locked the disk laser to a frequency comb, which in turn was combined to a 10 MHz recommendation,” stresses Rattunde.In their experiments, the scientists set the emission wavelength precisely to the target wavelength for presentation experiments at the fiber link of Saarland University (2062.40 nm), to which Fraunhofer IAF has actually turned over the laser module. In addition to power scaling, the most important research jobs of Fraunhofer IAF in the HiFi project are the exact understanding of the mode behavior of the lasers and the identification and elimination of noise sources.Quantum frequency conversion utilizing pump lasersIn quantum frequency conversion, the energy of the pump photon is deducted from the signal photon by a difference frequency process in a non-linear optical crystal. To guarantee a low-noise process, the energy of the pump photons should be below the target wavelength (generally 1550 nm), otherwise the pump laser can produce photons in the output signal due to parasitic effects.In combination with the MENLO frequency comb, the VECSELs established at Fraunhofer IAF satisfy the high requirements of quantum frequency conversion, as their narrow bandwidth and wavelength stability prevent variations in the pump wavelength and consequently changes in the target wavelength of the qubits. If there is a discrepancy above the natural linewidth, the qubits would no longer be identical, which would eliminate a basic requirement for subsequent quantum mechanical processing.
Quantum frequency conversion, essential for an international quantum Internet, is being advanced by the HiFi project, which tackles wavelength inequalities and stabilizes quantum interactions. These consist of much more powerful quantum computing through the connecting of quantum processors and signs up, more protected communication through quantum key distribution or more accurate time measurements through the synchronization of atomic clocks.However, the differences in between the glass fiber requirement of 1550 nm and the system wavelengths of the various quantum bits (qubits) understood to date represent a hurdle, due to the fact that those qubits are mostly in the visible or near-infrared spectral range. Credit: © Fraunhofer IAFProject HiFi: Enabling technologies for quantum frequency conversionIn the joint project “HiFi– Highly incorporated quantum frequency converter of greatest fidelity based on innovative laser, fiber and production technology” moneyed by the German Federal Ministry of Education and Research (BMBF), scientists are working on the awareness of all needed technologies to offer quantum frequency converters (QFK) with high effectiveness and low sound for initial test tracks.
