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MIT and Harvard Engineers Use “DNA-Legos” To Construct Graphene Nanostructures

This news is a follow-up to an earlier post “Harvard Researchers Create Self-Assembling Nano Bricks Made of DNA.”

Engineers are now using  self-assembling DNA nanobricks as a scaffold to build nanostructures out of graphene.

The MIT and Harvard researchers are essentially taking these shapes and binding them to a graphene surface with a molecule called aminopyrine.

Once bound, the DNA is coated with a layer of silver, and then a layer of gold to stabilize it. The gold-covered DNA is then used as a mask for plasma lithography, where oxygen plasma burns away the graphene that isn’t covered. Finally, the DNA mask is washed away with sodium cyanide, leaving a piece of graphene that is an almost-perfect copy of the DNA template.

So far, the researchers have used this process — dubbed metallized DNA nanolithography — to create X and Y junctions, rings, and ribbons out of graphene.

Nanoribbons, which are simply very narrow strips of graphene, are of particular interest because they have a bandgap — a feature that graphene doesn’t normally possess. A bandgap means that these nanoribbons have semiconductive properties, which means they might one day be used in computer chips.

Graphene rings are also of interest, because they can be fashioned into quantum interference transistors — a new and not-well-understood transistor that connects three terminals to a ring, with the transistor’s gate being controlled by the flow of electrons around the ring.

(via MIT and Harvard engineers create graphene electronics with DNA-based lithography | ExtremeTech)

Quantum Photonics: Researchers Develop Technique to Transmit Data As Twisted Streams of Light

In terms of these quantum states, photons possess two distinct polarization orientations, along with a theoretically infinite number of helical wave forms, in which the photons rotate around the direction they’re moving. The latter have garnered a lot of interest, as they could potentially carry a lot more data than other optical methods.

Possible applications include quantum computing, improved fiber optic communication, point-to-point data transfer across free space, and microscopy.

Researchers have now developed a way to produce twisted light beams using silicon chips, the starting point for compact, efficient optical communication.

Xinlun Cai and colleagues shaped photons using a microscopic, ring-shaped grating, which sent twisted light out in a specified pattern. Each ring was small enough to be fabricated into integrated circuits, and capable of emitting multiple vortexes of light simultaneously. The same type of chip could also serve as a receiver for twisted light, and manipulate waves that transit through it.

(via Fabbing a chip that could encode data in a twisted vortex of light | Ars Technica)

Major Quantum Computing Milestone: Physicists Build Single-Atom Quantum Bit in Silicon

Some of the popular approaches to building quantum computers include confining atoms in cryogenic gases to create quantum bits (or qubits) and using superconducting circuits.

In 1998, Bruce Kane, a physicist at the University of Maryland, in College Park, suggested an approach based on solid-state silicon semiconductors that are doped with phosphorus. He proposed using the quantum characteristic of spin in the nucleus of the phosphorus donor atom as the qubit.

Many scientists were enamored with this idea, because it showed the potential to integrate quantum computers with conventional silicon processing.

Morello and Dzurak were among the physicists impressed by Kane’s proposal, but they chose to investigate electron spins instead, because electron spins in silicon have very long coherence times—that is, it takes a relatively long time for such a qubit to lose its information.

In 2010, they demonstrated the ability to read the state of an electron’s spin. Basically, they managed to get the spin state of the electron to control the flow of electrons in a nearby circuit and produce a digital readout.

Now, Morello and Dzurak have discovered how to write the spin state. This completes the two-stage process required to operate a quantum bit. They managed to do this by using a microwave field to gain unprecedented control over an electron bound to a single phosphorous atom, which was implanted next to a specially designed silicon transistor.

(via Physicists Build First Single-Atom Quantum Bit in Silicon - IEEE Spectrum)

Major Quantum Computing Milestone Hit: Shows How Much Remains to Be Done

Believe it or not, deriving that 15=3x5 with 48% accuracy is a big deal.

For the first time, a functional solid-state quantum computer has completed a fairly simple math problem, factoring a prime number into its constituent parts. The solution itself isn’t that great an accomplishment — it was the number 15 — but it’s a major leap for quantum computers, because it’s a step toward factoring much larger numbers.

…The team built a quantum circuit made of four superconducting qubits, which are the logic gates of a quantum system, on top of a substrate made of sapphire. It also contained five microwave resonators. The fabrication itself was a breakthrough, because organizing nine separate quantum pieces required very precise, automated construction methods.

The qubits were entangled and verified using quantum experiments. Then the team used this circuit to factor 15 using Peter Shor’s factoring algorithm. That code says for any given integer N, the computer must find its prime factors. But it does this quantum-fast, finding the solution exponentially faster than the quickest known classical factoring algorithm.

(via Quantum Processor Calculates That 15 = 3x5 (With Almost 50% Accuracy!) | Popular Science)

Researchers Figuring out How to Read Quantum States Without Altering Them

“Normally, every contact with the outer world changes information in a quantum mechanical system in a completely uncontrolled manner,” explains Professor Mario Ruben from Karlsruhe Institute of Technology. “We therefore have to keep the quantum state stable and shielded. On the other hand, information has to be read out in a controlled manner for further use.”

Magnetic molecule complexes may be a solution of this dilemma. In their center, a metal atom with a pronounced magnetic moment, a spin, is located. It is surrounded by organic molecules that shield the atom.

“When synthesizing this protective enclosure, we can exactly define how much the metal atom sees of the outer world,” explains Ruben.

The study is based on the metal atom terbium, using an enclosure of about 100 carbon, nitrogen, and water atoms and placed in the center of nanometer-sized, electric gold contacts. The electrodes had an effect similar to the three channels of a transistor. Electric voltage of the middle gate electrode influenced the current through the other two electrodes. In this way, the working point was set.

The molecule was then exposed to various changing magnetic fields and the jump of the spin was reflected by the amplitude of the current curve. “By measuring current flow, we found that the nuclear spin of the metal atom is stable for up to 20 seconds,” says Ruben. “For quantum mechanical processes, this is a very long time.”

(via Electronic readout of quantum bits for spintronics and quantum computing | KurzweilAI)

Effect Precedes Cause in Real-World Quantum Entanglement Demonstration

A real-world demonstration of a thought experiment conducted at the University of Vienna, has produced a result that is somewhat befuddling to people with what the lead researcher calls a “naïve classical world view.”

Two pairs of particles are either quantum-entangled or not. One person makes the decision as to whether to entangle them or not, and another pair of people measure the particles to see whether they’re entangled or not.

The head-scratcher is: the measurement is made before the decision is made, and it is accurate. “Classical correlations can be decided after they are measured,” says Xiao-song Ma, the writer of the study. Entanglement can be created “after the entangled particles have been measured and may no longer exist.”

(via In New Quantum Experiment, Effect Happens Before Cause | Popular Science)

Researchers Claim Breakthrough in Quantum Computing

Researchers say they have designed a tiny crystal that acts like a quantum computer so powerful it would take a computer the size of the known universe to match it.

Details of the crystal, which is made up of just 300 atoms, are published today in the journal Nature.

“Quantum computing is a kind of information science that is based on the notion that if one performs computations in a fundamentally different way than the way your classical desktop computer works,” says study co-author University of Sydney’s Dr Michael Biercuk.

“There’s a huge potential to solve a variety of problems that are very, very hard or near impossible for standard computer.”

The crystal simulator uses a property of quantum mechanics called superposition, where a quantum particle appears to be in two distinct states at the same time. This means the particle, known as a qubit, can be used to solve two equations simultaneously.

As the number of qubits increase, the number or states increases exponentially. For example, 2 qubits can simultaneously be in 4 states, 3 qubits in 8 states: 2 to the power of n states for n qubits.

[Photo Source: Britton/NIST]

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(scinerds via futurist-foresight)

Progress in Quantum Computing

Computer scientists have built a superconducting number cruncher with a Von Neumann architecture that paves the way for a new era of quantum computation

(via First Quantum Computer With Quantum CPU And Separate Quantum RAM - Technology Review)

(via futuramb)

a team of scientists from Australia and Japan have successfully transferred a complex set of quantum data in light form. You see, previously researchers had struggled with slow performance or loss of information, but with full transmission integrity achieved — as in blocks of qubits being destroyed in one place but instantaneously resurrected in another, without affecting their superpositions — we’re now one huge step closer to secure, high-speed quantum communication.

(via First light wave quantum teleportation achieved, opens door to ultra fast data transmission)