Tag Archives: Stefan Maier

Seeing quantum objects with the naked eye

This research is a collaborative effort between the Polytechnique de Montréal (or École polytechnique de Montréal; Canada) and the Imperial College of London (UK) according to a July 14, 2015 news item on Nanotechnology Now,

For the first time, the wavelike behaviour of a room-temperature polariton condensate has been demonstrated in the laboratory on a macroscopic length scale. This significant development in the understanding and manipulation of quantum objects is the outcome of a collaboration between Professor Stéphane Kéna-Cohen of Polytechnique Montréal, Professor Stefan Maier and research associate Konstantinos Daskalakis of Imperial College London. …

A July 14, 2015 Polytechnique de Montréal news release supplies an explanation of this ‘sciencish’ accomplishment,

Quantum objects visible to the naked eye

Quantum mechanics tells us that objects exhibit not only particle-like behaviour, but also wavelike behaviour with a wavelength inversely proportional to the object’s velocity. Normally, this behaviour can only be observed at atomic length scales. There is one important exception, however: with bosons, particles of a particular type that can be combined in large numbers in the same quantum state, it is possible to form macroscopic-scale quantum objects, called Bose-Einstein condensates.

These are at the root of some of quantum physics’ most fascinating phenomena, such as superfluidity and superconductivity. Their scientific importance is so great that their creation, nearly 70 years after their existence was theorized, earned researchers Eric Cornell, Wolfgang Ketterle and Carl Wieman the Nobel Prize in Physics in 2001.

A trap for half-light, half-matter quasi-particles

Placing particles in the same state to obtain a condensate normally requires the temperature to be lowered to a level near absolute zero: conditions achievable only with complex laboratory techniques and expensive cryogenic equipment.

“Unlike work carried out to date, which has mainly used ultracold atomic gases, our research allows comprehensive studies of condensation to be performed in condensed matter systems under ambient conditions” explains Mr. Daskalakis. He notes that this is a key step toward carrying out physics projects that currently remain purely theoretical.

To produce the room-temperature condensate, the team of researchers from Polytechnique and Imperial College first created a device that makes it possible for polaritons – hybrid quasi-particles that are part light and part matter – to exist. The device is composed of a film of organic molecules 100 nanometres thick, confined between two nearly perfect mirrors. The condensate is created by first exciting a sufficient number of polaritons using a laser and then observed via the blue light it emits. Its dimensions can be comparable to that of a human hair, a gigantic size on the quantum scale.

“To date, the majority of polariton experiments continue to use ultra-pure crystalline semiconductors,” says Professor Kéna-Cohen. “Our work demonstrates that it is possible to obtain comparable quantum behaviour using ‘impure’ and disordered materials such as organic molecules. This has the advantage of allowing for much simpler and lower-cost fabrication.”

The size of the condensate is a limiting factor

In addition to directly observing the organic polariton condensate’s wavelike behaviour, the experiment showed researchers that ultimately the condensate size could not exceed approximately 100 micrometres. Beyond this limit, the condensate begins to destroy itself, fragmenting and creating vortices.

Toward future polariton lasers and optical transistors

In a condensate, the polaritons all behave the same way, like photons in a laser. The study of room-temperature condensates paves the way for future technological breakthroughs such as polariton micro-lasers using low-cost organic materials, which are more efficient and require less activation power than  conventional lasers. Powerful transistors entirely powered by light are another possible application.

The research team foresees that the next major challenge in developing such applications will be to obtain a lower particle-condensation threshold so that the external laser used for pumping could be replaced by more practical electrical pumping.

Fertile ground for studying fundamental questions

According to Professor Maier, this research is also creating a platform to facilitate the study of fundamental questions in quantum mechanics. “It is linked to many modern and fascinating aspects of many-body physics, such as Bose-Einstein condensation and superfluidity, topics that also intrigue the general public,” he notes.

Professor Kéna-Cohen concludes: “One fascinating aspect, for example, is the extraordinary transition between the state of non-condensed particles and the formation of a condensate. On a small scale, the physics of this transition resemble an important step in the formation of the Universe after the Big Bang.”

Here’s a link to and a citation for the paper,

Spatial Coherence and Stability in a Disordered Organic Polariton Condensate by K. S. Daskalakis, S. A. Maier, and S. Kéna-Cohen Phys. Rev. Lett. 115 (3), 035301 DOI: 10.1103/PhysRevLett.115.035301 Published 13 July 2015

This article is behind a paywall but there is an earlier open access version  here: http://arxiv.org/pdf/1503.01373v2.

Are we creating a Star Trek world? T-rays and tricorders

There’s been quite a flutter online (even the Huffington Post has published a piece) about ‘Star Trek-hand-held medical scanners’ becoming possible due to some recent work in the area of T-rays. From the Jan. 20, 2012 news item on Nanowerk,

Scientists who have developed a new way to create a type of radiation known as Terahertz (THz) or T-rays – the technology behind full-body security scanners – say their new, stronger and more efficient continuous wave T-rays could be used to make better medical scanning gadgets and may one day lead to innovations similar to the “tricorder” scanner used in Star Trek.

In a study published recently in Nature Photonics (“Greatly enhanced continuous-wave terahertz emission by nano-electrodes in a photoconductive photomixer” [behind a paywall]), researchers from the Institute of Materials Research and Engineering (IMRE), a research institute of the Agency for Science, Technology and Research (A*STAR) in Singapore and Imperial College London in the UK have made T-rays into a much stronger directional beam than was previously thought possible and have efficiently produced T-rays at room-temperature conditions. This breakthrough allows future T-ray systems to be smaller, more portable, easier to operate, and much cheaper.

For anyone who’s not familiar with ‘Star Trek world’ and tricorders, here’s a brief description from a Wikipedia essay about tricorders,

In the fictional Star Trek universe, a tricorder is a multifunction handheld device used for sensor scanning, data analysis, and recording data.

David Freeman in his Jan. 21, 2012 article for the Huffington Post about the research puts it this way,

Trekkies, take heart. A scientific breakthrough involving a form of infrared radiation known as terahertz (THz) waves could lead to handheld medical scanners reminiscent of the “tricorder” featured on the original Star Trek television series.

What’s the breakthrough? Using nanotechnology, physicists in London and Singapore found a way to make a beam of the”T-rays”–which are now used in full-body airport security scanners–stronger and more directional.

Here’s how the improved T-ray technology works (from the Jan. 20, 2012 news item on Nanowerk),

In the new technique, the researchers demonstrated that it is possible to produce a strong beam of T-rays by shining light of differing wavelengths on a pair of electrodes – two pointed strips of metal separated by a 100 nanometre gap on top of a semiconductor wafer. The unique tip-to-tip nano-sized gap electrode structure greatly enhances the THz field and acts like a nano-antenna that amplifies the THz wave generated. The waves are produced by an interaction between the electromagnetic waves of the light pulses and a powerful current passing between the semiconductor electrodes from the carriers generated in the underlying semiconductor. The scientists are able to tune the wavelength of the T-rays to create a beam that is useable in the scanning technology.

Lead author Dr Jing Hua Teng, from A*STAR’s IMRE, said: “The secret behind the innovation lies in the new nano-antenna that we had developed and integrated into the semiconductor chip.” ….

Research co-author Stefan Maier, a Visiting Scientist at A*STAR’s IMRE and Professor in the Department of Physics at Imperial College London, said: “T-rays promise to revolutionise medical scanning to make it faster and more convenient, potentially relieving patients from the inconvenience of complicated diagnostic procedures and the stress of waiting for accurate results. Thanks to modern nanotechnology and nanofabrication, we have made a real breakthrough in the generation of T-rays that takes us a step closer to these new scanning devices. …”

It’s another story about handheld (or point-of-care) diagnostic devices and I have posted on this topic previously:

  • Jan. 4, 2012 about work in Alberta;
  •  Dec. 22, 2011 on grants to scientists in the US and Canada working on these devices;
  •  Aug. 4, 2011 about a diagnostic device the size of a credit card;
  •  Mar. 1, 2011 about nanoLAB from Stanford University (my last sentence in that posting “It’s not quite Star Trek yet but we’re getting there.”); and,
  •  Feb. 5, 2011 about the Argento and PROOF initiatives.

I see I had four articles last year and this year (one month old), I already have two articles on these devices. It reflects my own interest, as well as, the amount work being done in this area.