Photonic quantum computers and new generation optical quantum sensors require special light, and therefore special devices.
My research group spent 10 years at the University of Hamburg, before that, at Leibniz University Hannover, pioneering laser systems research and development and measuring instruments for the second quantum revolution.
Since 2010, “squeeze lasers” from my working group have been used in the GEO600 gravitational wave detector. Since 2019, my technique has improved the sensitivity of Rigo and Virgo. The same technology is currently available in a compact form. This means that the advantages of quantum correlation can be transferred to common laser measurement techniques and provide the basis for new lights in photonic quantum computers.
Comparison of laser light from the first and second quantum revolutions
The laser light from the previous first quantum revolution shows no quantum correlation. Therefore, it is not suitable for photonic quantum computers or new generation optical quantum sensors. This applies to all previous commercial lasers. Measurements are evident that there is no quantum correlation. For example, the number of photons per microsecond in measurement time can be explained by count statistics for individual random events.
If quantum correlation is present, the first photon measurement is followed by a fixed pattern of photons. This kind of laser light is a prominent figure in the second quantum revolution. But how is this laser light produced? And what are the requirements for the measuring device?
Measuring equipment
The required measuring equipment problems can be answered relatively easily. To fully reproduce quantum correlations in the measured signal, each photon must be converted
To a single well-defined electrical signal. This is because missed photons lead to clearly partially resolved quantum correlations. Similar damage occurs when additional electrical signals are generated without photons.
Nearly 100% quantum efficiency and dark count disappearing speed are required. One type of measuring device is optimized to measure high optical amplification and complex quantum correlations. These are what are called balanced homodin detectors. Other measurement devices have been optimized to count individual photon events. These are what are called single photon detectors.
Quantum correlation, production of “aperture” laser light
Different optical quantum technologies require different quantum correlations. However, in all cases it starts with the generation of the same fundamental quantum correlation, a well-defined “slanted vacuum state” of the laser beam. Because a spatially well-defined laser beam is required, two such beams have a high interference contrast, allowing for continuous generation of more complex quantum correlations. Laser systems that generate light beams in a narrowed vacuum state are usually made up of crystals between two mirrors. The energy source is a very pure pump laser beam.
Figure 1 shows a photograph of these optical components. In this photo, a second mirror is deposited directly on the convex polished back of the crystal. The clearly visible wavelength of the pump light here is 532 nm. A special property of crystals is that the electricly charged components of that atoms cannot be traced one-to-one to the vibrations of the green pump light. This creates important vibrational components of half the frequency, leading to light with a wavelength of 1064 nm. Quantum correlation is due to the fact that due to energy conservation, each photon at a wavelength of 532 nm can only be converted to two exact photons with a wavelength of 1064 nm.
A complete measuring device does not always measure one photon with this laser beam. There are 4, 6, and even more photons due to inductive ejection. ² These quantum correlation laser light is in a so-called “slanted vacuum state.” It is also simply called “squeezed light.” The term “squeezed” is a technical term here. Heisenberg’s principle of uncertainty to explain this light is motivated by the fact that it can be shown as a “squeezed” circle, not as a circle. We proposed to call such a laser system a “squeeze laser.”
Possibility of squeezed light and squeeze lasers
The sensitivity of laser sensors, which already operate with traditional laser light, which are already very stable, can be further improved with reduced light. This is especially important when the conventional power of light cannot be increased any further. This is exactly what it is because the Gravity Wave Observatory (GWOS) operates near thermal and photomechanical instability. In life sciences and medicine, light power is often limited by samples. The dimmed light also helps to maintain the safety of the laser. Due to the nature of quantum physics, laser sensors, which already use a lot of light, can only improve sensitivity by using narrowed light. This is also true for GWOS. Two compressed laser beams allow quantum encryption to be raised to a higher level of security in optical networks of several kilometers in size. Once the entanglement is generated, not only the communication channel but also the receiver’s measurement device is mathematically fixed. Universal, fault-resistant, scalable photonic quantum computers require compression light as the basis for generating more complex quantum correlations. Without a diaphragm state, we cannot realize a new, highly promising approach to photonic quantum computers.
Spin-off from the University of Hamburg: Noisy Labs Gmbh
Noisy Labs GmbH is a spin-off in the second generation of quantum technology at the University of Hamburg. Noisy Labs GmbH is the world’s first company to provide laser systems that produce well-defined laser beams in a vacuum condition.
Available wavelengths are 1064 nm and 1550 nm. Figure 2 illustrates such a system. The footprint is 60 x 40cm². Noisy Labs GmbH also offers a balanced homodin detector with guaranteed quantum efficiency of over 95%.
reference
The relationship between the wavelength λ and the frequency f of light is c =λ∙f. Here, c is the speed of light. The energy of a photon is proportional to the frequency of light. e =h∙F, proportional constant h, where Planck’s constant photon number is specified according to measurement time, Fourier limit spectral width R. Schnabel and A. Schoenbeck, “Squeeze Laser”, Transactions on Quantum Engineering: Quantum Sensing and Metrology 3, 3500209 (2022) exceeded a comencied collaborator Shot-Noise Limit’, Nature Physics 7, 962 (2011) H. Vahlbruch, M. Mehmet, K. Danzmann, R. Schnabel, ‘Detection of 15dB limiting light states for absolute calibration of photoelectron quantum efficiency and its applications’, Phys. Pastor Lett 117, 110801 (2016)
This article will also be featured in the 22nd edition of Quarterly Publication.
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