Turning up the heat on quantum mechanics

Scientists have made a startling prediction about the quantum world that seems to show that simply taking the temperature of certain types of quantum systems at frequent intervals causes such systems to break one of the hard and fast rules of thermodynamics.

Anyone who has dabbled in quantum mechanics will know just how slippery is the atomic and sub-atomic world of probability wave-functions where particles eddy and swirl like waves.

Gershon Kurizki

Gershon Kurizki

One of the underlying rules of the quantum world is the Time-Energy Uncertainty Principle. Wrapped up in this apparently simple phrase is the notion that it is impossible to know both the precise duration of any process and its exact energy cost in an atomic or subatomic particle with 100 % certainty; the very act of observing one or the other somehow disturbing the counterpart property.

The quantum world is spooky, to say the least.

Quantum systems run hot and cold when you take their temperature regularly (Credit: Gershon Kurizki)

Quantum systems run hot and cold when you take their temperature regularly (Credit: Gershon Kurizki)

Now, the laws of thermodynamics are apparently irrefutable, after all they allow sceptics to see straight through the claims of those inventors who claim perpetual motion machines, they allow us to build power stations, and ultimately they will take us to the ends of the universe.

One law reveals that the interaction between a large heat source and a cluster of smaller systems will, on average, move progressively towards thermal equilibrium – hot moves to cold to even out the temperature, in other words; this is the so-called zero’th law of thermodynamics. But, it ain’t necessarily so in the quantum world claim Weizmann chemists Gershon Kurizki, Noam Erez and Goren Gordon of the Weizmann Institute in Rehovot, Israel, working with Mathias Nest of Potsdam University, Germany. They have shown that an ensemble of quantum systems in thermal contact with a large heat source could buck this thermodynamic trend.

Their predictions suggest that such a quantum ensemble could actually heat up even if it is hotter than a neighbouring large heat source or if it is colder, it could get colder still, but only under certain conditions. The scientists showed that if the energy of these systems is measured repeatedly, both systems and large heat source will undergo a temperature increase or decrease, and this change depends only on the rate of measurement, not on the results of the measurements themselves.

In the classical world, a thermometer does not interfere with the laws of thermodynamics no matter how hot or cold a system nor how often the thermometer is read, but taking the temperature of a quantum system somehow decouples it from the neighbouring heat source. This decoupling, followed by recoupling of the two when measurement ceases, introduces energy (at the expense of the measuring apparatus) into the systems and the heat source alike, and so heats them up. Depending on whether the measurements are repeated at short or long intervals, it should be possible to heat up or cool down the systems.

The predicted effects may be the key to developing novel heating and cooling schemes for microscopic solid-state devices, such as quantum computer chips or in allowing ultrafast temperature control for fast optical measurements in the chemistry laboratory.

Further reading

Nature, 2008, 452, 724-727
http://dx.doi.org/10.1038/nature06873

Weizmann Institute Quantum Optics Group homepage
http://www.weizmann.ac.il/chemphys/gershon/

Mathias Nest homepage
http://tcb16.chem.uni-potsdam.de/nest/

Suggested searches

thermodynamics
quantum mechanics

Want optical chips with that?

Ever-smaller and ever-faster microelectronics devices with increased storage space, more communications and other functions, and much-reduced battery usage, are part of the incentive behind research into photonic crystals. These materials are bringing us closer to a technologically viable optical transistor that will form the building blocks of future optoelectronics that use photons instead of electrons to process information.

The optical properties of photonic crystals vary in a regular pattern on a scale of hundreds of nanometres. This physical structure means that light entering a photonic crystal can be controlled. For instance, a photonic crystal can transmit light of one particular wavelength, and block all others.

Rana Biswas

Rana Biswas

The simplest material of this kind has a layered structure, like a film of oil on water. Such one-dimensional structures are used as mirrors, non-reflective coatings, and paints whose colours change with the viewing angle. While nature does not exactly abound with photonic crystals, the natural gemstone, opal, is a photonic crystal, which is what gives it its unique shifting and shimmering colours. Synthetic photonic crystals have been on the science agenda since the nineteenth century, but it is only with the advent of modern fabrication techniques that designer 3D photonic crystals have become attainable.

Optical computers aside, there is a second thread woven into the fabric of photonic crystal research – telecommunications.

Now, researchers at the US Department of Energy’s Ames Laboratory have come up with what might be the perfect way to sort and distribute vast quantities of data through optical fibres. The new technology is based on a filter constructed from a three-dimensional photonic crystal and could allow multiple wavelength channels to be carried along the same stretch of optical fibre without loss and without error. The so-called add-drop filter could ultimately give us the all-optical transmission links that require no electronic components along the route.

There are up to 160 wavelength channels travelling through an optical fibre at the same time, explains Ames physicist Rana Biswas, That means a lot of dialogue is going on simultaneously. He adds that as data is carried along the fibre it is necessary to drop off individual wavelength channels at different points.

When the data being transported in multiple frequency channels over an optical fibre comes to a receiving station, you want to be able to pick off just one of those frequencies and send it to an individual end user, explains Biswas, That’s where these 3D photonic crystals come into play. The same filter technology will also allow optimal use of the fibre’s bandwidth.

The idea of add-drop filters was first conceived in the 1990s, but work focused on 2D photonic crystals until now. The Ames team created a 3D photonic crystal device that contains an entrance waveguide and an exit waveguide for channelling light, which means there is none of the light intensity loss seen with 2D photonics.

There is still at least one hurdle to jump before the 3D add-drop filter can be used in fibre optic communications and that is to scale down the device to the wavelengths of light used in Internet communications – 1.5 micrometres. That remains a big challenge confesses Biswas.

Further reading

Rana Biswas homepage
http://cmp.ameslab.gov/personnel/biswas/bio.html

Feature on photonic crystals from ICT Results
http://cordis.europa.eu/ictresults/index.cfm/section/news/tpl/article/id/89575

Suggested searches

photonic crystals
fibre optics
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Hubble Beater

Cambridge and Caltech astronomers have devised a new digital sensor for their telescopes that effectively cancels out the twinkling caused by the Earth’s atmosphere and allows them to obtain pictures of distant heavenly bodies that are clearer even than those obtained by space telescopes, such as Hubble.

Everyone knows the nursery rhyme, Twinkle, twinkle, little star, none are more frustrated by it than ground-based astronomers hoping to probe the depths of space. Even in the clearest air atop an Andean mountain, the stars still twinkle. Luckily there is now hope for the vertically challenged telescope user in the form of a new high-speed, almost noise-free digital camera developed by a team at the Institute of Astronomy in Cambridge led by Craig Mackay working with Caltech’s Nick Law and his group.

A Lucky break lights up new stars

A Lucky break lights up new stars

Previously, astronomers have tried to develop adaptive optics to correct the blurring caused by atmospheric distortion of the light from distant stars entering a telescope. Unfortunately, these devices have only proven themselves in the infrared region of the spectrum where twinkling can be cancelled out effectively. It is the visible region that has left ground-based astronomers envious of the images obtained by the Hubble Space Telescope. Until now.

The new camera works by recording a sequence of images at twenty frames per second or faster. The system software then checks each image, selects the sharpest and least smeared images and then the images are combined to cancel out the random fluctuations using a technique the team calls Lucky Imaging. The technique is similar to that used to cancel random noise in other areas of science such as spectroscopy, where a sequence of spectra for the same sample are recorded, added together and the peaks and troughs of noise cancel each other out.

Clearer view of the Cat’s Eye Nebula with Lucky Camera

Clearer view of the Cat’s Eye Nebula with Lucky Camera

The team has tested the method with the 5.1 m telescope at Mount Palomar. With its conventional imaging sensors, the telescope produces images an order of magnitude less detailed than those from Hubble. With the Lucky Camera in place, the team was able to obtain images that are actually twice as sharp as those produced by Hubble, all without leaving the comfort of planet Earth. These are the sharpest images ever taken either from the ground or from space, say the researchers, To get sharper pictures you have to use an even bigger telescope. Indeed, they are now investigating the possibility of getting Lucky with the 8.2 m Very Large Telescope of the European Southern Observatory in Chile and the 10 m Keck telescopes on the top of Mauna Kea in Hawaii.

So far, the team has already discovered many multiple star systems which are too close together and too faint to find with any standard telescope. Stars separated by as short a distance as one light-day have been resolved in images of the globular star cluster M13 which lies at a distance of some 25,000 light-years from earth

Further reading

Dr Craig Mackay homepage
http://www.ast.cam.ac.uk/~optics/people/cdm.htm

Lucky image homepage
http://www.ast.cam.ac.uk/~optics/Lucky_Web_Site/index.htm

Suggested searches

telescopes
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