QUANTUM COMPUTING--MORE FAST AND MORE RELIABLE!!

Combining physics, mathematics and computer science, quantum computing has developed in the past two decades from a visionary idea to one of the most fascinating areas of quantum mechanics. The recent excitement in this lively and speculative domain of research was triggered by Peter Shor (1994) who showed how a quantum algorithm could exponentially “speed-up” classical computation and factor large numbers into primes much more rapidly (at least in terms of the number of computational steps involved) than any known classical algorithm. Shor's algorithm was soon followed by several other algorithms that aimed to solve combinatorial and algebraic problems, and in the last few years theoretical study of quantum systems serving as computational devices has achieved tremendous progress.

While computers have been around for the majority of the 20th century, quantum computing was first theorized less than 30 years ago, by a physicist at the Argonne National Laboratory. Paul Benioff is credited with first applying quantum theory to computers in 1981. Benioff theorized about creating a quantum Turing machine. Most digital computers are based on the Turing Theory.

Defining the Quantum Computer

The Turing machine, developed by Alan Turing in the 1930s, is a theoretical device that consists of tape of unlimited length that is divided into little squares. Each square can either hold a symbol (1 or 0) or be left blank. A read-write device reads these symbols and blanks, which gives the machine its instructions to perform a certain program. Does this sound familiar? Well, in a quantum Turing machine, the difference is that the tape exists in a quantum state, as does the read-write head. This means that the symbols on the tape can be either 0 or 1 or a superposition of 0 and 1; in other words the symbols are both 0 and 1 (and all points in between) at the same time. While a normal Turing machine can only perform one calculation at a time, a quantum Turing machine can perform many calculations at once.

Today's computers, like a Turing machine, work by manipulating bits that exist in one of two states: a 0 or a 1. Quantum computers aren't limited to two states; they encode information as quantum bits, or qubits, which can exist in superposition. Qubits represent atoms, ions, photons or electrons and their respective control devices that are working together to act as computer memory and a processor. Because a quantum computer can contain these multiple states simultaneously, it has the potential to be millions of times more powerful than today's most powerful supercomputers.

This superposition of qubits is what gives quantum computers their inherent parallelism. According to physicist David Deutsch, this parallelism allows a quantum computer to work on a million computations at once, while your desktop PC works on one. A 30-qubit quantum computer would equal the processing power of a conventional computer that could run at 10 teraflops (trillions of floating-point operations per second). Today's typical desktop computers run at speeds measured in gigaflops (billions of floating-point operations per second).

Quantum computers also utilize another aspect of quantum mechanics known as entanglement. One problem with the idea of quantum computers is that if you try to look at the subatomic particles, you could bump them, and thereby change their value. If you look at a qubit in superposition to determine its value, the qubit will assume the value of either 0 or 1, but not both (effectively turning your spiffy quantum computer into a mundane digital computer). To make a practical quantum computer, scientists have to devise ways of making measurements indirectly to preserve the system's integrity. Entanglement provides a potential answer. In quantum physics, if you apply an outside force to two atoms, it can cause them to become entangled, and the second atom can take on the properties of the first atom. So if left alone, an atom will spin in all directions. The instant it is disturbed it chooses one spin, or one value; and at the same time, the second entangled atom will choose an opposite spin, or value. This allows scientists to know the value of the qubits without actually looking at them.

The Qubit

A bit is the basic unit of computer information. Regardless of its physical realization, a bit is always understood to be either a 0 or a 1. An analogy to this is a light switch— with the off position representing 0 and the on position representing 1.

A qubit has some similarities to a classical bit, but is overall very different. Like a bit, a qubit can have two possible values—normally a 0 or a 1. The difference is that whereas a bit must be either 0 or 1, a qubit can be 0, 1, or a superposition of both.

Theoretically, a single qubit can store an infinite amount of information, yet when measured it yields only the classical result (0 or 1) with certain probabilities that are specified by the quantum state. In other words, the measurement changes the state of the qubit, “collapsing” it from the superposition to one of its terms. The crucial point is that unless the qubit is measured, the amount of “hidden” information it stores is conserved under the dynamic evolution (namely, Schrödinger's equation). This feature of quantum mechanics allows one to manipulate the information stored in unmeasured qubits with quantum gates, and is one of the sources for the putative power of quantum computers.

Quantum Gates

Classical computational gates are Boolean logic gates that perform manipulations of the information stored in the bits. In quantum computing these gates are represented by matrices, and can be visualized as rotations of the quantum state on the Bloch sphere. This visualization represents the fact that quantum gates are unitary operators, i.e., they preserve the norm of the quantum state (if U is a matrix describing a single qubit gate, then U^†U=I, where U^† is the adjoint of U, obtained by transposing and then complex-conjugating U). As in the case of classical computing, where there exists a universal gate (the combinations of which can be used to compute any computable function), namely, the NAND gate which results from performing an AND gate and then a NOT gate, in quantum computing it was shown (Barenco et al., 1995) that any multiple qubit logic gate may be composed from a quantum CNOT gate (which operates on a multiple qubit by flipping or preserving the target bit given the state of the control bit, an operation analogous to the classical XOR, i.e., the exclusive OR gate) and single qubit gates. One feature of quantum gates that distinguishes them from classical gates is that they are reversible: the inverse of a unitary matrix is also a unitary matrix, and thus a quantum gate can always be inverted by another quantum gate.

Quantum Circuits

Quantum circuits are similar to classical computer circuits in that they consist of wires and logical gates. The wires are used to carry the information, while the gates manipulate it (note that the wires do not correspond to physical wires; they may correspond to a physical particle, a photon, moving from one location to another in space, or even to time-evolution). Conventionally, the input of the quantum circuit is assumed to be a computational basis state, usually the state consisting of all 0. The output state of the circuit is then measured in the computational basis, or in any other arbitrary orthonormal basis. The first quantum algorithms (i.e. Deutsch-Jozsa, Simon, Shor and Grover) were constructed in this paradigm. Additional paradigms for quantum computing exist today that differ from the quantum circuit model in many interesting ways. So far, however, they all have been demonstrated to be computationally equivalent to the circuit model (see below), in the sense that any computational problem that can be solved by the circuit model can be solved by these new models with only a polynomial overhead in computational resources.

Today's Quantum Computers

Quantum computers could one day replace silicon chips, just like the transistor once replaced the vacuum tube. But for now, the technology required to develop such a quantum computer is beyond our reach. Most research in quantum computing is still very theoretical.

The most advanced quantum computers have not gone beyond manipulating more than 16 qubits, meaning that they are a far cry from practical application. However, the potential remains that quantum computers one day could perform, quickly and easily, calculations that are incredibly time-consuming on conventional computers. Several key advancements have been made in quantum computing in the last few years. Let's look at a few of the quantum computers that have been developed.

1998

Los Alamos and MIT researchers managed to spread a single qubit across three nuclear spins in each molecule of a liquid solution of alanine (an amino acid used to analyze quantum state decay) or trichloroethylene (a chlorinated hydrocarbon used for quantum error correction) molecules. Spreading out the qubit made it harder to corrupt, allowing researchers to use entanglement to study interactions between states as an indirect method for analyzing the quantum information.

2000

In March, scientists at Los Alamos National Laboratory announced the development of a 7-qubit quantum computer within a single drop of liquid. The quantum computer uses nuclear magnetic resonance (NMR) to manipulate particles in the atomic nuclei of molecules of trans-crotonic acid, a simple fluid consisting of molecules made up of six hydrogen and four carbon atoms. The NMR is used to apply electromagnetic pulses, which force the particles to line up. These particles in positions parallel or counter to the magnetic field allow the quantum computer to mimic the information-encoding of bits in digital computers.

Researchers at IBM-Almaden Research Center developed what they claimed was the most advanced quantum computer to date in August. The 5-qubit quantum computer was designed to allow the nuclei of five fluorine atoms to interact with each other as qubits, be programmed by radio frequency pulses and be detected by NMR instruments similar to those used in hospitals (see How Magnetic Resonance Imaging Works for details). Led by Dr. Isaac Chuang, the IBM team was able to solve in one step a mathematical problem that would take conventional computers repeated cycles. The problem, called order-finding, involves finding the period of a particular function, a typical aspect of many mathematical problems involved in cryptography.

2001

Scientists from IBM and Stanford University successfully demonstrated Shor's Algorithm on a quantum computer. Shor's Algorithm is a method for finding the prime factors of numbers (which plays an intrinsic role in cryptography). They used a 7-qubit computer to find the factors of 15. The computer correctly deduced that the prime factors were 3 and 5.

2005

The Institute of Quantum Optics and Quantum Information at the University of Innsbruck announced that scientists had created the first qubyte, or series of 8 qubits, using ion traps.

2006

Scientists in Waterloo and Massachusetts devised methods for quantum control on a 12-qubit system. Quantum control becomes more complex as systems employ more qubits.

2007

Canadian startup company D-Wave demonstrated a 16-qubit quantum computer. The computer solved a sudoku puzzle and other pattern matching problems. The company claims it will produce practical systems by 2008. Skeptics believe practical quantum computers are still decades away, that the system D-Wave has created isn't scaleable, and that many of the claims on D-Wave's Web site are simply impossible (or at least impossible to know for certain given our understanding of quantum mechanics).

If functional quantum computers can be built, they will be valuable in factoring large numbers, and therefore extremely useful for decoding and encoding secret information. If one were to be built today, no information on the Internet would be safe. Our current methods of encryption are simple compared to the complicated methods possible in quantum computers. Quantum computers could also be used to search large databases in a fraction of the time that it would take a conventional computer. Other applications could include using quantum computers to study quantum mechanics, or even to design other quantum computers.

But quantum computing is still in its early stages of development, and many computer scientists believe the technology needed to create a practical quantum computer is years away. Quantum computers must have at least several dozen qubits to be able to solve real-world problems, and thus serve as a viable computing method.

Source-- www.howstuffworks.com

Physicists at The University of Texas at Austin, in collaboration with colleagues in Taiwan and China, have developed the world's smallest semiconductor laser, a breakthrough for emerging photonic technology with applications from computing to medicine.

Miniaturization of semiconductor lasers is key for the development of faster, smaller and lower energy photon-based technologies, such as ultrafast computer chips; highly sensitive biosensors for detecting, treating and studying disease; and next-generation communication technologies.

Such photonic devices could use nanolasers to generate optical signals and transmit information, and have the potential to replace electronic circuits. But the size and performance of photonic devices have been restricted by what's known as the three-dimensional optical diffraction limit.

"We have developed a nanolaser device that operates well below the 3-D diffraction limit," said Chih-Kang "Ken" Shih, professor of physics at The University of Texas at Austin. "We believe our research could have a large impact on nanoscale technologies."

In the current paper, Shih and his colleagues report the first operation of a continuous-wave, low-threshold laser below the 3-D diffraction limit. When fired, the nanolaser emits a green light. The laser is too small to be visible to the naked eye.

The device is constructed of a gallium nitride nanorod that is partially filled with indium gallium nitride. Both alloys are semiconductors used commonly in LEDs. The nanorod is placed on top of a thin insulating layer of silicon that in turn covers a layer of silver film that is smooth at the atomic level.

It's a material that the Shih lab has been perfecting for more than 15 years. That "atomic smoothness" is key to building photonic devices that don't scatter and lose plasmons, which are waves of electrons that can be used to move large amounts of data.

"Atomically smooth plasmonic structures are highly desirable building blocks for applications with low loss of data," said Shih.

Nanolasers such as this could provide for the development of chips where all processes are contained on the chip, so-called "on-chip" communication systems. This would prevent heat gains and information loss typically associated with electronic devices that pass data between multiple chips.

"Size mismatches between electronics and photonics have been a huge barrier to realize on-chip optical communications and computing systems," said Shangjr Gwo, professor at National Tsing Hua University in Taiwain and a former doctoral student of Shih's.

Physicists Explore Properties of Electrons in Revolutionary Material

Scientists from Georgia State University and the Georgia Institute of Technology have found a new way to examine certain properties of electrons in graphene -- a very thin material that may hold the key to new technologies in computing and other fields.

Ramesh Mani, associate professor of physics at GSU, working in collaboration with Walter de Heer, Regents' Professor of physics at Georgia Tech, measured the spin properties of the electrons in graphene, a material made of carbon atoms that is only one atom thick.

The research was published this week in the online-only journal Nature Communications.

Electrons, which follow orbits around the nucleus in atoms, have two important characteristics -- charge and spin.

The electric charge is the basis of most electronic devices, but spin -- which Mani and co-workers examined using a new technique -- forms the basis of new "spintronic" devices, and can serve as a building block for new computers in a field called quantum computing, as well as other technologies.

Graphene is thought to be a key material for spintronic devices, but it is so new that scientists must perform a lot of research on it to understand its capability. The GSU and Georgia Tech study propels this research forward.

"We tried to use the electrical resistance to detect spin resonance. When you shine microwaves on the device, and the microwave energy equals the spin-splitting energy," Mani explained.

"The device absorbs the microwave energy, and that changes the resistance of the device. But this is usually such a small effect that one hardly expects to see it. Fortunately, this material allowed us to see the effect. Measuring spin resonance electrically is especially useful for nanoscale devices."

"By doing such a measurement, we can measure properties like the spin splitting energy, and the spin relaxation time directly," he continued. "There have been other measurements, but those have been a little more indirect."

With the advance in measuring the properties of an electron's spin in graphene, it will allow scientists to carry out further studies of this novel material -- giving researchers ways to optimize graphene for spintronic applications.

Mani noted that that the experiments which were conducted at GSU, were very labor intensive. Simply creating graphene -- which de Heer's laboratory accomplished -- is very time consuming and requires enormous experience.

Measurements use very sophisticated equipment, requiring the researchers to immerse samples in liquid Helium at temperatures close to absolute zero -- about 460 degrees Fahrenheit below zero.

Atlanta has become a center for graphene research, Mani said.

"The confluence of available experimental capability in Atlanta, a hotbed for graphene science and technology, made possible this important advance in the world of spintronics physics," he explained.

The team included Mani of GSU, de Heer, John Hankinson and Claire Berger of Georgia Tech.

Source:- http://www.sciencedaily.com

Original Journal:-Ramesh G Mani, John Hankinson, Claire Berger, Walter A de Heer. Observation of resistively detected hole spin resonance and zero-field pseudo-spin splitting in epitaxial graphene. Nature Communications, 2012; 3: 996 DOI:

New Silicon Memory Chip May Offer Super-Fast Memory

The first purely silicon oxide-based 'Resistive RAM' memory chip that can operate in ambient conditions -- opening up the possibility of new super-fast memory -- has been developed by researchers at UCL.

Resistive RAM (or 'ReRAM') memory chips are based on materials, most often oxides of metals, whose electrical resistance changes when a voltage is applied -- and they "remember" this change even when the power is turned off.

ReRAM chips promise significantly greater memory storage than current technology, such as the Flash memory used on USB sticks, and require much less energy and space.

The UCL team have developed a novel structure composed of silicon oxide, described in a recent paper in the Journal of Applied Physics, which performs the switch in resistance much more efficiently than has been previously achieved. In their material, the arrangement of the silicon atoms changes to form filaments of silicon within the solid silicon oxide, which are less resistive. The presence or absence of these filaments represents a 'switch' from one state to another.

Unlike other silicon oxide chips currently in development, the UCL chip does not require a vacuum to work, and is therefore potentially cheaper and more durable. The design also raises the possibility of transparent memory chips for use in touch screens and mobile devices.

The team have been backed by UCLB, UCL's technology transfer company, and have recently filed a patent on their device. Discussions are ongoing with a number of leading semiconductor companies.

Dr Tony Kenyon, UCL Electronic and Electrical Engineering, said: "Our ReRAM memory chips need just a thousandth of the energy and are around a hundred times faster than standard Flash memory chips. The fact that the device can operate in ambient conditions and has a continuously variable resistance opens up a huge range of potential applications.

"We are also working on making a quartz device with a view to developing transparent electronics."

For added flexibility, the UCL devices can also be designed to have a continuously variable resistance that depends on the last voltage that was applied. This is an important property that allows the device to mimic how neurons in the brain function. Devices that operate in this way are sometimes known as 'memristors'.

This technology is currently of enormous interest, with the first practical memristor, based on titanium dioxide, demonstrated in just 2008. The development of a silicon oxide memristor is a huge step forward because of the potential for its incorporation into silicon chips.

The team's new ReRAM technology was discovered by accident whilst engineers at UCL were working on using the silicon oxide material to produce silicon-based LEDs. During the course of the project, researchers noticed that their devices appeared to be unstable.

UCL PhD student, Adnan Mehonic, was asked to look specifically at the material's electrical properties. He discovered that the material wasn't unstable at all, but flipped between various conducting and non-conducting states very predictably.

Adnan Mehonic, also from the UCL Department of Electronic and Electrical Engineering, said: "My work revealed that a material we had been looking at for some time could in fact be made into a memristor.

"The potential for this material is huge. During proof of concept development we have shown we can programme the chips using the cycle between two or more states of conductivity. We're very excited that our devices may be an important step towards new silicon memory chips."

The technology has promising applications beyond memory storage. The team are also exploring using the resistance properties of their material not just for use in memory but also as a computer processor.

The work was funded by the Engineering and Physical Sciences Research Council.

Source- http://www.sciencedaily.com

Li-Fi INSTEAD OF Wi-Fi?

"DATA TRANSMISSION THROUGH VISIBLE LIGHT POSSIBLE, says researchers"

Many of us are familiar with Wi-Fi technology and its impact in our daily lives. We cannot survive without it. Wi-Fi is being used everywhere like in repair shops, educational institutes, computer shops, offices. We have become quite dependent upon this technology that we can hardly imagine our life without it.

Wi-Fi technology can cover an entire home and it is band limited to 50-100 megabits per second today using IEEE802.11n standard. This is a good standard to use current services provided by internet like browsing and moving larger data files like softwares, HD movies, video games, music libraries etc. It may be very useful in today’s life but it may not be that efficient in future where we have a gesture recognition technology coming.

So here comes in the new technology names as VISIBLE LIGHT COMMUNICATION or simply VLC. It is more frequently referred to as Li-Fi(Light Fidelity).

This emerging new technology offers optical wireless communication by using visible light. An additional opportunity is arising by using current state-of-the-art LED lighting solutions for illumination and communication as the same time and with the same module. Hence when the LEDs are illuminating, their secondary duty will be to communicate data onto lighting system. This will be relevant in the indoor systems where the light will be fully ‘on’.

The premise behind VLC is that since light is always on and we have reflections everywhere communications can ride along for nearly free. The VLC technology include giga-speed technology, optical mobility technologies, navigation, precision location and gesture recognition technology.

For giga-speed technology, the Li-Fi Consortium defined GigaDock, GigaBeam, GigaShower, Giga Spot and GigaMIMO models to address different user scenarios for wireless indoor and indoor like data transfers. While GIgaDock is a wireless docking solution including wireless charging for smartphones, tablets or notebooks, with speeds upto 10Gbps, the GigaBeam model is a point to point data link for kiosk applications or portable-to-portable data exchanges. Thus a two hour full HD movie, whose size can be imagines around 5GB, can be transferred from one device to other in merely 4 seconds!

First applications of Li-Fi have already been put to use in hospitals where RF signals are a threat due to interference problems with medical equipment such as blood pumps and other life supporting instruments. The prototype of a mobile phone with an incorporated VLC system was presented by Casio in Las Vegas earlier this year. In coming years we are surely going to see more of the Li-Fi technology and more compatible products entering the market from labs.

Infinite number of wireless channels possible in a fixed bandwidth

Infinite number of wireless channels possible in a fixed bandwidth

Italian researchers have demonstrated in Venice a technique which could allow the implementation of an infinite number of channels in a given, fixed bandwidth.

“We have experimentally shown that by using helicoidal parabolic antennae, the use of OAM (orbital angular momentum) states might dramatically increase the capacity of any frequency band, allowing the use of dense coding techniques in each of these new vortex radio channels,” say the researchers, “this might represent a concrete proposal for a possible solution to the band saturation problem.”

Most of the researchers are from the University of Padova, with one from the Swedish Institute of Space Physics and one from the Padova Nanofabrication Laboratory.

The experimental transmission, from the isle of San Giorgio across the water to the Doge’s Palace – a distance of 442m - showed  that it is possible to use two beams of incoherent radio waves, transmitted on the same frequency but encoded in two different orbital angular momentum states, to simultaneously transmit two independent radio channels.

The location of the experiment was chosen because it is where Galileo first demonstrated his invention of the telescope 400 years ago.

The technique could be used in TV broadcasts, WiFi and radio.

‘This novel radio technique allows the implementation of, in principle, an infinite number of channels in a given, fixed bandwidth, even without using polarization, multiport or dense coding techniques,’ say the researchers in a paper describing the experiment, ‘this paves the way for innovative techniques in radio science and entirely new paradigms in radio communication protocols that might offer a solution to the problem of radio-band congestion.’

Source: Epoch Times