Tag Archives: Quantum

Chinese Researchers Teleport Entangled States Through Nearly 100 Km!

The spooky action-at-a-distance just got a lot longer – over six times longer. Though, the phenomenon is not yet ‘Beam me up, Scotty’, the improvement is heartening. A team of Chinese researchers have teleported qubits across a distance of 97 kilometers, using the phenomenon of entanglement.

The spooky entangled world

Entanglement is a purely quantum-mechanical phenomenon, which started on its road to stardom and fame within the physics community and outside it due to a thought experiment by Einstein.

Here it is in simple terms and closely in the same spirit as Einstein, Podolsky and Rosen had first put it. Take two electron. Now, if they are in the same quantum state, one has to be in an ‘up’ spin state and the other in a ‘down’ spin state. The two spins cannot be the same, because another fundamental principle of quantum mechanics – the Pauli exclusion principle – forbids that. Now, take one electron and separate it from the other by a very large distance – say half the universe – but without ever ‘looking’ at it to see what spin state it is in. Now, take the electron near you and look at it to determine what the spin is. But if you know that, you immediately know what spin state the other electron is in! In other words, you get the information about the farther electron instantaneously, violating the fundamental postulate of relativity which forbids the transfer of information faster than light speed.

To EPR or not to EPR

There has been plenty of debates on this so-called EPR paradox. It remained a thought experiment until Alain Aspect and his group actually performed the experiment and found that entanglement is a very real phenomenon. That hasn’t doused the debates though, with people trying to determine what information actually means and whether information is actually transferred.

Photons entangled

Now, the Chinese team uses photons, just like Alain Aspect’s team did in their pioneering experiment. They created two entangled photons, using a 1.3 watt laser, and made them appear at two distinct places separated by as much as 97 kilometers!

Now, a photon can represent a quantum state – or a number of quantum states, really – and can thus be thought of as a ‘qubit’ or quantum bit. It carries a ‘bit’ of information, just like a ‘bit’ on the hard disk of a computer. So far, the researchers have been able to transmit the ‘key’ to a encrypted message, but the message itself needs to be sent via classical channels. It’s like mailing a locked treasure-chest and sending the key to the lock via a quantum mechanically entangled channel.

The work has just been put on ArXiv and here is the link: http://arxiv.org/abs/1205.2024

IBM Researchers Make Quantum Computing a Reality

IBM announced in a press release yesterday, that they have made  “major advances in quantum computing device performance that may accelerate the realization of a practical, full-scale quantum computer.” Such a computer would run circles around any supercomputer in existence today.

IBM made their presentation at the March meeting of the American Physical Society. Quantum computing has been a dream scientists have been chasing for years. The problem is that when you hear the word “quantum” you’re dealing with atomic and subatomic particles. These particles have a tendency to be unstable. IBM researchers have made huge strides in getting these tiny particles to stabilize. The practical applications for quantum computing are seemingly endless. The reason is because quantum bits can be made to exist in several states at once where traditional bits used in today’s computers have basically two states, on and off. These multiple states will give computers the ability to compute millions of simultaneous computations. Check out the video below to see the concept explained by IBM researchers.

The exciting thing about this announcement from IBM is that the quantum computer is not as far away as we once thought. What was once thought to be 50 years off is now possibly 10 – 15 years away. Having this kind of computing power will help us with predicting weather, unlocking mysteries of the human genome, and even help secure computers with massive encryption. It’s like the future is now!

AT&T Rolls Out The WP7 NoDo Update For The Samsung Focus

Microsoft started rolling out the NoDo update bringing the much awaited copy & paste feature to all WP7 handsets, at the end of the last month.

However, some carriers decided to delay the release of the NoDo update for WP7 based handsets including AT&T.

Nevertheless, AT&T has finally started rolling out the NoDo update for the Samsung Focus and the LG Quantum. The HTC Surround will get its NoDo update sometime in May, due to some software issues.

Samsung_Focus

Samsung has also taken this opportunity to roll out a firmware update for the Focus. The new firmware update incorporates some useful changes and bug fixes.

The capacitive buttons on the Focus are temporarily disabled, if an app is open and a   user drags his finger from the screen to the buttons. This will definitely be appreciated by all Focus owners, and will help in reducing all those accidental touches. No more going back to the previous screen, while playing Fruit Ninja!

Another nifty change brought by this firmware is the anti-shake setting being enabled by default for the Camera. Most users don’t really bother to check out the camera settings before clicking a snap, and this small change will definitely come in handy for them.

WP7 is a closed OS, still users need to wait for sometime before they can update their handset to the latest version of the OS.   So much for being a closed OS!

Via WPCentral

Quantum Breakthrough: Matter Guided through Optical Guides, Just Like Light Through Optical Fibers

It’s atoms now, and not only light. Researchers at ARC Center of Excellence for Quantum Atom Optics, Research School of Physics, ANU, have successfully guided supercooled Helium atoms through an optical guide made of a laser beam. This is the first ever successful at guiding matter waves.

Speckles, Modes and the Rest of the Basics:

When light is guided in an optical fiber, there can be many modes of transmission. These modes interfere and produce a speckle pattern’ on the screen after emerging from the fiber. The light can be adjusted so as to eliminate the speckle, which indicates that the light is in a single mode, or technically, coherent’. Scientists say that the light has the same phase factor’ throughout, which doesn’t vary with time.

Laser Speckle
Laser Speckle, the indication of multiple modes

There are many other coherent substances that can be made. One of them is known as the Bose-Einstein Condensate (BEC). During the 1920’s, Satyendranath Bose and Albert Einstein worked out the statistics of bosons and showed that, if cooled enough, they can be made to fall into a single giant ground state. In this state, any addition to the number density of the particles makes more particles fall into the ground state. This is, thus, called a Condensate’, appropriately named, Bose-Einstein Condensate’.

Bose Einstein Condensate
Bose-Einstein Condensate (The peaks indicate the number density of atoms in the ground state. Note how it rises with fall in temperature) (nK=nanoKelvin) (Courtesy: Colorado University)

BEC is a remarkable state of matter. Thousands of bosons (for example, Helium atoms) can condense and behave like a single super-atom. BEC physics is one of the richest and the present interest is primarily because BEC physics mimics that of superconductors.

The guiding of matter waves

What the team of researchers has achieved is this: They took a bunch of atoms and trapped them. Then,  they irradiated this with laser light pointing downwards towards gravity. This produced a speckled pattern.

As Ken Baldwin, one of the team members, reports

We have shown that when atoms in a vacuum chamber are guided inside a laser light beam, they too can create a speckle pattern – an image of which we have captured for the first time.

The BEC guide
The schematic for the BEC guide used by the researchers. (Courtesy: Nature)

The atoms were cooled to lower and lower temperatures, until the atoms formed the BEC. Since the BEC is a coherent state, with the lowering of the intensity of the laser light, the speckled pattern suddenly disappeared.

Team leader, Dr. Andrew Truscott, reported that:

The atoms … behaved more like waves than particles, forming a Bose-Einstein condensate (BEC).   When the BEC was loaded into the guide, the speckle pattern disappeared, showing that just one mode was being transmitted the single quantum wave.

Looking at the images and by measuring the arrival times of the atoms on the Multi-Channel Plate (MCP), the researchers could differentiate between a speckled, multi-mode transmission and a smooth, single-mode transmission.

Achievement:

Earlier it was only light that could be guided in a wave guide (here, the optical fiber). No longer is that true. This breakthrough demonstrates that it is possible to guide atoms in a BEC state in an optical guide (not glass). This will allow higher precision atom-interferometers.

Neutrons in Demand:Scientists Develop New Method To Probe Quantum Gravity

A brand new method to measure gravity and minute quantizations in a gravitational field that uses neutrons entrapped between two vibrating parallel plates immersed in a gravitational field, has been developed by scientists at the University of Technology, Vienna (TU Vienna). Neutrons have earlier been used for electromagnetic (EM) field measurements, but similar methods are now being used to measure gravity, a force which is 10-36 times (i.e. one in a billion billion billion billion parts) as strong as the EM force.

Neutron Probe for Gravity
(Courtesy: physorg.com

The physics

Any field which can be quantized (EM can be quantized; gravity cannot be quantized as yet) contains discrete energy levels, which can be occupied by quantum particles. A particle cannot occupy a space between two successive levels. It may, however, jump (technically, make a transition’) from one quantum state to another, giving off radiation in the process.

A quantum particle in a certain state needs to be excited with just the right amount of energy so that it can make transition to a higher energy state. This process is called resonance’.

For quantizing any field, it has to be bounded in space within some finite range. This is conveniently achieved by limiting the extent of the experimental apparatus between two parallel plates. These plates may even be used to induce transitions, as we will see below.

The method

To probe gravitational fields, neutrons are being confined between two closely spaced parallel plates, which can be vibrated at very precise frequencies. If gravity can, indeed, be quantized, then each of the neutrons sits in one of the energy levels in the gravitational field. By vibrating the plates at a very precise frequency (the resonant’ frequency), just the right amount of energy can be pumped into the system. This energy will then be taken up by the neutrons, which will jump’ to higher quantum levels. By measuring the resonance peaks in the vibrational spectrum, scientists hope to accurately map out the quantum levels in the gravitational field.

Extremely cold neutrons are used instead of atoms or electrons, because they are heavy particles and also uncharged. They are unaffected by EM fluctuations, are nearly non-polarizable and are unaffected by the Casimir force.

Gravity and its Quantization

The problem of trying to quantize gravity started with Einstein, when only the EM force had been quantized. Since then, the weak and the strong forces have been quantized and unified into a single theory. Gravity has survived all attempts of quantization and unification. A primary problem with gravity is that the static space-time background present for the other forces is itself distorted by gravity. (In fact, relativity says that the distortion of space-time is gravity). The results of this experiment might give valuable clues as to the energy scales needed for unification. This may also demonstrate the very limits of possibility of a unified theory (like string theory and its many versions).

Calabi fields
String theory demands extra dimensions, which might be curled up

Implications

The experiment is much smaller in scale than the existent LIGO and can be performed in a laboratory. Questions still remain as to how fine the measurements need to be in order to be fully sure of the result.

The experiment also hopes to verify the validity of the equivalence principle (which says that gravitational and inertial masses are exactly the same) at extremely small length and energy scales. This principle is crucial for the correctness of general relativity (GR), and thus will deliver a verdict on the applicability of GR at quantum scales. A more sophisticated version of the experiment might even be used to probe into the nature of dark matter, but that is still some time away.

No one is sure if this will work, but as Pauli said, He who dares, wins.