The novel system developed in the MPG Junior Research Group "Laboratory of Photonics" led by Dr. Tobias Kippenberg could resolve this problem (Nature Photonics, DOI 10.1038/nphoton.2008.199, Advance online publication, 28 September 2008). The scientists succeeded in developing a micron-scale on-chip resonator which allows for optimized mechanical and optical quality even though these quantities in general have opposing requirements. The system combines the world`s best optical and mechanical coherence properties and its sensitivity could be used for basic research such as exploring the quantum behaviour of tangible micron-scale objects as well as for applications such as further improving frequency and time standards.
The glass microresonator (blue) combines the world\'s best properties of optics and mechanics. On the one hand it stores photons which can circulate around its outer rim for hundreds of thousand times before leaving it again. The eventually emerging photons allow extremely accurate measurements of the mechanical oscillations of the resonator. The optimized support of the glass structure via four nano-spokes strongly decouples its mechanical oscillations from the environment. Excited mechanical modes can thus oscillate up to 80\'000 times before decaying. MPQ
At the beginning of the previous century seminal work of Werner Heisenberg gave birth to the theory of quantum mechanics. It dictates that mechanical motion is quantized -- from the microscopic motion of electrons around nuclei to the macroscopic behaviour of everyday objects. It was only in 1986 -- more than 60 years after Heisenberg's initial work -- that quantum jumps of individual electrons leading to the characteristic emission spectra of atoms could be directly observed. Ten years later, the advances in laser techniques and quantum optics allowed also observing non-classical motional states of individually trapped ions -- which can be 100'000 times heavier than electrons. However a fundamental question has remained: Why don't also larger objects which we deal with in our daily lives follow the rules of quantum mechanics but behave classically instead?
It is generally assumed that decoherence prevents us from observing quantum effects in macroscopic objects. Decoherence subsumes the fact that interaction with the environment disturbs and eventually destroys the quantum behaviour of individual systems which -- well isolated -- would be expected to behave according to the laws of quantum mechanics. Today, quantum mechanical effects have never been observed in tangible, mesoscopic oscillators, i.e. objects consisting of trillions of atoms. This goal requires a combination of well isolated mechanical systems and a coherent readout technique whose sensitivity is sufficient to observe quantum effects.
Quartz oscillators which are used e.g. in wristwatches exhibit high mechanical coherence and would thus satisfy the former criterion. The electrical circuits which are used to read out their mechanical motion, however, at the moment offer insufficient sensitivity which makes this route towards observing possible quantum effects virtually impassable. Many research groups therefore pursue combining highly coherent mechanical systems with quantum optical methods which offer incomparably higher sensitivity. But this approach faces the challenge that the requirements for optical and mechanical coherence often oppose each other.
The group of Dr. Tobias Kippenberg at MPQ was able for the first time to combine the world's best optical and mechanical coherence properties in a single on-chip resonator. In their experiment the scientists used toroidal glass resonators with a diameter of about 75µm mounted on a silicon chip which were produced in the cleanrooms of the Ludwig-Maximilians-University Munich (LMU) at the chairs of Prof. Jörg Kotthaus and Prof. Jochen Feldmann. Via glass nanofibers laser light is coupled into the toroids.
The strong coupling of optical and mechanical degrees of freedom renders these structures very special. The system can store light, i.e. photons, orbiting around the torus if its wavelength "fits" into the toroid, that is when the torus' circumference is an integer multiple of the wavelength. The mechanical oscillations modulate the toroid's circumference and thus imprint themselves on the optical resonance frequency. On the other hand the circulating photons exert a force on the toroid pointing radially outwards.
The mechanical eigenmodes of the resonators experience friction forces of different origins which determine the coupling to the environment leading to decoherence. The mechanical clamping of the structure to its support plays a very important role in this process. The experiments showed that the different mechanical modes of the toroids can couple to each other and the support in a complicated fashion. Elucidating this coupling was the key to understanding the losses caused by friction. These could be considerably reduced by mounting the toroid on the silicon chip via glass "nano-spokes" (cf. Fig.). By optimizing the geometry, i.e. the length and width of the spokes Rémi Rivière and Georg Anetsberger, lead author of the study, could "tailor" the eigenmodes of the resonator leading to a 1000-fold reduction of clamping losses.The thus optimized microtoroids can store photons for hundreds of thousands of orbits. At the same time they perform up to 80'000 mechanical oscillations before these decay due to the interaction with the environment. In a sense this system can be compared to quartz oscillators which can be driven by light (instead of electrical current) and read out by a resonant optical circuit.
"This is the first system which allows controlling optical and mechanical degrees of freedom within a chip-scale device. For the first time we were able to combine mechanical quality factors rivalling those achieved in nano- and microelectronics with the highest values of optical quality", says Georg Anetsberger. This represents a major step towards the long term goal of observing quantum mechanical effects in a macro-scopic oscillator. But beyond the fundamental importance, the research may also impact technology.
Mechanical quartz oscillators are ubiquitous in science and technology and understanding dissipation is at the heart of any improvement in terms of the oscillators' stability for timekeeping -- whether in a wristwatch or as flywheel in an atomic clock. [G.A.]Original publication:
Dr. Olivia Meyer-Streng | idw
DGIST develops 20 times faster biosensor
24.04.2017 | DGIST (Daegu Gyeongbuk Institute of Science and Technology)
New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
24.04.2017 | Physics and Astronomy
24.04.2017 | Materials Sciences
24.04.2017 | Life Sciences