Light and Atoms Get Entangled

All I can say about this development is "WOW!!!"

31 January 2006

Physicists have for the first time entangled two atomic quantum bits, or "qubits", that are separated by long distances. Alex Kuzmich, Brian Kennedy and colleagues at the Georgia Institute of Technology in the US did this by entangling an atomic qubit with a photon, sending the photon down an optical fibre to a neighbouring lab, and then converting the photon into another atomic qubit. Meanwhile, Harald Weinfurter and co-workers at the Max-Planck Institute for Quantum Optics in Garching and the Ludwig-Maximilians University in Munich have entangled an atom with a photon at a wavelength suitable for low-loss communication over long distances.

Entanglement allows particles to have a much closer relationship than is possible in classical physics: if two particles are entangled, we can know the state of one particle by measuring the state of the other. For example, two particles can be entangled such that the polarization of one particle is always "horizontal" when the spin of the other is "vertical", and vice versa; or that the spin of one particle is "up" when the other is "down", and vice versa. An additional feature of quantum mechanics is that the particle can exist in a superposition of both these states at the same time. By taking advantage of such quantum phenomena, a quantum computer could, in principle, outperform a classical computer for certain tasks.

Although physicists can now routinely entangle photons and send them over long distances down optical fibres, these particles are difficult to store for long periods and so are not ideal as qubits for real quantum information systems. In contrast, qubits based on ground-state atoms have long lifetimes and so can be stored. Kuzmich and colleagues have now succeeded in remotely entangling two such atomic qubits using a photon (Phys. Rev. Lett. 96 030405).

The Georgia Tech team made each long-lived qubit using "collective" spin states of a cold cloud of about 100,000 rubidium-85 atoms. Only a single spin is "flipped" in these collective states but the flip is distributed over all of the atoms involved in the qubit. The physicists began by preparing an entangled state of one of these atomic qubits and a single photon in a magneto-optical trap in their laboratory.

Next, the scientists transmitted the photon down an optical fibre to a magneto-optical trap in another lab located 5.5 metres away. Finally, they converted the photon into another atomic qubit, also consisting of rubidium-85 atoms. The team then measured the resulting entanglement of the two atomic qubits by "transferring" their quantum states onto photons and then measuring the polarization correlations of the photons.

"It should now be possible to teleport quantum states of matter over long distances," says Kuzmich. "The breakthrough also indicates that atoms and photons can be used for larger quantum networks -- though further work on practical issues is still necessary."

Meanwhile, in a separate experiment, Weinfurter and colleagues have entangled a single trapped atom with a single photon at a wavelength of 0.78 microns, which is suitable for low-loss communication over long distances, using similar experimental techniques to the Georgia Tech group (Phys. Rev. Lett. 96 030404). The entanglement is between the polarization of the photon and the internal site of a rubidium-87 atom stored in an optical trap. Kuzmich and colleagues have also demonstrated atom-photon entanglement at "telecommunications" wavelengths of 1.5 microns.

Peering More Deeply into the Quantum World

Another big step in the evolution of metrology tools from researchers at Georgia Tech.

New Device Revolutionizes Nano Imaging
Much faster technology allows AFM to capture nano movies, create material properties images

ATLANTA (February 9, 2006) — While a microphone is useful for many things, you probably wouldn’t guess that it could help make movies of molecules or measure physical and chemical properties of a material at the nanoscale with just one poke.

Georgia Tech researchers have created a highly sensitive atomic force microscopy (AFM) technology capable of high-speed imaging 100 times faster than current AFM. This technology could prove invaluable for many types of nano-research, in particular for measuring microelectronic devices and observing fast biological interactions on the molecular scale, even translating into movies of molecular interactions in real time. The research, funded by the National Science Foundation and the National Institutes of Health, appears in the February issue of Review of Scientific Instruments.

Not only is FIRAT™ (Force sensing Integrated Readout and Active Tip) much faster than AFM (the current workhorse of nanotech), it can capture other measurements never before possible with AFM, including material property imaging and parallel molecular assays for drug screening and discovery. FIRAT could also speed up semiconductor metrology and even enable fabrication of smaller devices. It can be added with little effort to existing AFM systems for certain applications.

“I think this technology will eventually replace the current AFM,” said Dr. Levent Degertekin, head of the project and an asscoiate professor in the Woodruff School of Mechanical Engineering at Georgia Tech. “We’ve multiplied each of the old capabilities by at least 10, and it has lots of new applications.”

FIRAT solves two of AFM’s chief disadvantages as a tool for examining nanostructures — AFM doesn’t record movies and it can’t reveal information on the physical characteristics of a surface, said Dr. Calvin Quate, one of the inventors of AFM and a professor at Stanford University.

“It is possible that this device provides us with the ‘ubiquitous’ tool for examining nanostructures,” Quate added.

And what’s the key to this dramatic increase in speed and capabilities? A completely new microphone-inspired probe.

Current AFM scans surfaces with a thin cantilever with a sharp tip at the end. An optical beam is bounced off the cantilever tip to measure the deflection of the cantilever as the sharp tip moves over the surface and interacts with the material being analyzed.

FIRAT works a bit like a cross between a pogo stick and a microphone. In one version of the probe, the membrane with a sharp tip moves toward the sample and just before it touches, it is pulled by attractive forces. Much like a microphone diaphragm picks up sound vibrations, the FIRAT membrane starts taking sensory readings well before it touches the sample.

And when the tip hits the surface, the elasticity and stiffness of the surface determines how hard the material pushes back against the tip. So rather than just capturing a topography scan of the sample, FIRAT can pick up a wide variety of other material properties.

“From just one scan, we can get topography, adhesion, stiffness, elasticity, viscosity — pretty much everything,” Degertekin said.

For a regular AFM to detect the features of the object, the actuator must be large enough to move the cantilever up and down. The inertia of this large actuator limits the scanning speed of the current AFM. But FIRAT solves this problem by combining the actuator and the probe in a structure smaller than the size of a head of a pin. With this improvement, FIRAT can move over sample topography in a fraction of the time it takes AFM to scan the same area.

Georgia Tech researchers have been able to use FIRAT with a commercial AFM system to produce clear scans of nanoscale features at speeds as high as 60 Hertz (or 60 lines per second). The same system was used to image the topography as well as elastic and adhesive properties of carbon nanotubes simultaneously, which is another first.

FIRAT’s new speed and added features may open up many new applications for AFM.

For instance, FIRAT is capable of scanning integrated circuits for mechanical and material defects. And in biomolecular measurement applications, FIRAT can scan the surface quickly enough for a researcher to observe molecular interactions in real time.

“The potential is huge. AFM started as a topography tool and has exploded to many more uses since. I’m sure people will find all sorts of uses for FIRAT that I haven’t imagined,” Degertekin said.

FIRAT will be available for certain applications immediately, while others may take a few years, Degertekin said.

Remembering Hunt Taylor

For as he thinks in his heart, so is he.
(Proverbs 23:7, NKJV)

My dear friend and business partner, Hunt Taylor, passed away last Sunday in a tragic motorcycle accident in Arizona. He was 54 years young. All those that knew Hunt are mourning the devastating loss of a great man. I remember the first time I met Hunt. It was as if I had known him my entire life. Whenever you meet people like that, you know you are blessed.

Hunt was a terrific partner. He loved to think deeply about many things -- often unconventionally. He was, in that respect, Mungarian (I'm referring to Charlie Munger's "Lattice of Models" approach to investing). There was very little, in fact, that you couldn't discuss with Hunt. He was always open to new ideas.

Over the past several years, we discussed and debated (sometimes heatedly!) the emerging science of complexity, the mystery and beauty of quantum mechanics, the differences between risk and uncertainty, the future of the investment management business, the supply and demand for commodities, diamonds, oil, the prospects for nanotechnology and alternative forms of energy, the evolution of the music business and much more. I loved talking to Hunt. It always seemed as if we never had enough time together. I'm sure it was the same for many people in Hunt's life.

But what I loved most about Hunt was his heart. In my nearly two decades on Wall Street, I've learned that the heart is the most underappreciated and undervalued intangible asset. There's an old saying on Wall Street that if you want a friend, buy a dog. I didn't need to buy a dog. I had Hunt Taylor in my life, and I was blessed.

We will all deeply miss Hunt. But if you are like me, the love, laughter, and wisdom he shared will always live in your heart.