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The new device builds on the considerable work over the last two decades on trapped ion quantum computers. It consists of five ytterbium ions lined up and trapped in an electromagnetic field. The electronic state of each ion can be controlled by zapping it with a laser. This allows each ion to store a bit of quantum information.
Because they are charged, the ions exert a force on each other, and this causes them to vibrate at frequencies that can be precisely controlled and manipulated. These vibrations are quantum in nature and allow the ions to become entangled. In this way, the quantum bits they hold can interact.
By controlling these interactions, physicists can carry out quantum logic operations.
Time-bin encoding is a technique used... to encode a qubit of information on a photon.
The photon... is guided through one of two paths... (o)ne of the two paths is longer than the other. The difference in path length must be longer than the coherence length of the photon to make sure the path taken can be unambiguously distinguished.
If the photon has a non-zero probability to take either path, then it is in a coherent superposition of the two states.
To generate multiple frequencies, [researchers] sent the pulses through a tiny ring, called a microring resonator. The resonator generates photon pairs on a series of discrete frequencies, using spontaneous form-wave mixing, thus creating a frequency comb.
The interferometer the team used has one long arm and one short arm, and when a single photon comes out of the system, it is in a superposition of time states, as if it traveled through both the long arm and the short arm simultaneously. [i.e, time-bin encoded]
[The researchers] are the first to create photons with multiple frequencies using the same chip. This feature can enable multiplexed and multi-channel quantum communications and increased quantum computation information capacity.
Kues notes that the chip could improve quantum key distribution, a process that lets two parties share a secret key to encrypt messages with theoretically unbreakable security. It could also serve as a component of a future quantum computer.
The team is currently working to integrate the lasers, interferometer, and microring resonator of the device into a standard photonic chip, to build logic gates for quantum state manipulation, and to increase the degree of entanglement, which is a measure of the strength of the link between particles.
Eliot Kapit, an assistant professor of physics at Tulane University in New Orleans, has proposed a different approach to quantum error correction. His method takes advantage of a recently discovered unexpected benefit of quantum noise: when carefully tuned, quantum noise can actually protect qubits against unwanted noise. Rather than actively measuring the system, the new method passively and autonomously suppresses and corrects errors, using relatively simple devices and relatively little computing power.
In the absence of any errors, there are a pair of oscillating photon configurations that are the 'good' logical states of the device, and they oscillate at a fixed frequency based on the circuit parameters," Kapit explained...
When a photon randomly escapes from the circuit, the oscillation is broken, at which point a second, passive error correction circuit kicks in and quickly inserts two photons, one which restores the lost photon and reconstructs the oscillating logical state, and the other is dumped to a lossy circuit element and quickly leaks back out of the system. The combination of careful tuning of the resonant frequencies of the circuit and adding photons two at a time to correct losses ensures that the passive error correction circuit can operate continuously but won't do anything to the two good qubits unless their oscillation has been broken by a photon loss.
MIT research group claims that they developed a prototype of a Quantum computers with five atoms in an ion trap.
Much of the world’s digital data is currently protected by public key cryptography, an encryption method that relies on a code based partly in factoring large numbers. Computers have traditionally struggled to do the calculations based on factoring, so data transferred in this way remains secure...
Chuang and his collaborators found that the five-atom quantum computer successfully calculated the factors of 15. Previously, experts thought such a calculation would require at least 12 qubits to complete. Chuang says the five-ion model can be scaled up to factor much bigger numbers as long as the ion trap can hold its qubits in place. The team published its results in this week’s issue of Science.
Though a functional quantum computer of the necessary size to crack RSA encryption is still far off in the future, the threat that such a computer poses still resonates among digital security experts. In January, the U.S. National Security Agency posted a FAQ on the risks.
Chuang sees his experiment as an opportunity to point out vulnerabilities and push security experts to find even more secure solutions for the next generation
Accessing the computer, which is housed in a research lab in Yorktown Heights, New York, is relatively simple for anyone with basic understanding of computer programming. IBM offers a tutorial on how to use the service.
Using a simple quantum circuit, constructed on a 2-qubit photonics quantum processor, the researchers were able to outperform classical computers in certain highly specialised problems.
"An exciting outcome of our work is that we may have found a new example of quantum walk physics that we can observe with a primitive quantum computer, that otherwise a classical computer could not see," said Jonathan Matthews of the Centre for Quantum Photonics.
The team at MIT, led by Jagadeesh Moodera of the Department of Physics and postdoc Ferhat Katmis, was able to bond together several molecular layers of a topological insulator material called bismuth selenide (Bi2Se3) with an ultrathin layer of a magnetic material, europium sulfide (EuS). The resulting bilayer material retains all the exotic electronic properties of a TI and the full magnetization capabilities of the EuS.
But the big surprise was the stability of that effect. While EuS itself is known to retain its ability to hold a magnetic state only at extremely low temperatures, just 17 degrees above absolute zero (17 Kelvin), the combined material keeps those characteristics all the way up to ordinary room temperature.
The effect, which the researchers call proximity-induced magnetism, could also enable a new variety of “spintronic” devices based on a property of electrons called spin, rather than on their electrical charge. It might also provide the first practical way of producing a kind of particle called Majorana fermions, predicted by physicists but not yet observed convincingly. That in turn could help in the development of quantum computers, they say.
Researchers from the National University of Singapore (NUS) and the University of Strathclyde, UK, have become the first to test in orbit technology for satellite-based quantum network nodes.
They have put a compact device carrying components used in quantum communication and computing into orbit. And it works: the team report first data in a paper published 31 May 2016 in the journal Physical Review Applied.
The group's first device is a technology pathfinder. It takes photons from a BluRay laser and splits them into two, then measures the pair's properties, all on board the satellite. To do this it contains a laser diode, crystals, mirrors and photon detectors carefully aligned inside an aluminum block. This sits on top of a 10 centimetres by 10 centimetres printed circuit board packed with control electronics.
The team are working with standard "CubeSat" nanosatellites, which can get relatively cheap rides into space as rocket ballast. Ultimately, completing a global network would mean having a fleet of satellites in orbit and an array of ground stations.
[T]he researchers with this new effort have built an actual machine that is based on two of the strongest approaches to building a quantum computer.
The first approach is based on the gate model, where qubits are linked together to form primitive circuits that together form quantum logic gates. In such an arrangement, each logic gate is capable of performing one specific type of operation. Thus, to make use of such a computer, each of the logic gates must be programmed ahead of time to carry out certain tasks.
With the second approach the qubits do not interact, instead they are kept at a ground state where they are then caused to evolve into a system capable of solving a particular problem. The result is known as an adiabatic machine.
[T]o gain the positive attributes of both approaches by creating a machine where they started with a standard quantum computer and then used it to simulate an adiabatic machine. It uses 9 qubits and has over 1,000 logic gates and allows for communication between qubits to be turned on and off at will. The end result, the team reports, is one that unlike an adiabatic machine, is able to tackle traditionally difficult computing problems
Similar to a breadboard in electrical engineering
... A quantum box is an artificially produced structure that restricts a particle's movements, so that it can move in only two dimensions...
The research team refined an established method in which atoms are repositioned one after the other using scanning tunneling microscopy, allowing the creation of clearly defined quantum systems. Through the targeted relocating of xenon atoms in quantum boxes, the team succeeded in generating different patterns that correspond to a wide range of quantum states.
Handful of qubits. This arrangement of gold electrodes on a chip can hold up to twelve magnesium ions 40 micrometers above its surface while laser light cools them, enabling the ions to functions as qubits. Error-correction techniques allowing qubits to recover from unwanted disturbances.
To corral their quantum atoms into an orderly 3-D pattern for their experiments, the team constructed a lattice made by beams of light to trap and hold the atoms in a cubic arrangement of five stacked planes -- like a sandwich made with five slices of bread -- each with room for 25 equally spaced atoms. The arrangement forms a cube with an orderly pattern of individual locations for 125 atoms. The scientists filled some of the possible locations with qubits consisting of neutral cesium atoms -- those without a positive or a negative charge.
Weiss and his team then use another kind of light tool -- crossed beams of laser light -- to target individual atoms in the lattice. The focus of these two laser beams, called "addressing" beams, on a targeted atom shifts some of that atom's energy levels by about twice as much as it does for those of any of the other atoms in the array, including those that were in the path of one of the addressing beams on its way to the target. When the scientists then bathe the whole array with a uniform wash of microwaves, the state of the atom with the shifted energy levels is changed, while the states of all the other atoms are not.
We have set more qubits into different, precise quantum superpositions at the same time than in any previous experimental system," Weiss said. The scientists also designed their system to be very insensitive to the exact details of the alignments or the power of those light beams they use—which Weiss said is a good thing because "you don't want to be dependent upon exactly what the intensity of the light is or exactly what the alignment is."
"We changed the quantum superposition of the PSU atoms to be different from the quantum superposition of the other atoms in the array," Weiss said. "We have a pretty high-fidelity system. We can do targeted selections with a reliability of about 99.7%, and we have a plan for making that more like 99.99%."
Until recently, simple and low-cost quantum random number generators did not exist, preventing quantum physics from becoming the dominant source of randomness," the white paper states. "However, a number of manufacturers have now been able to address this challenge, leveraging quantum effects in a variety of ways to deliver the highest quality randomness, at high rates and at competitive costs."
NIST is taking the following steps to initiate a standardization effort in post-quantum cryptography. NIST plans to specify preliminary evaluation criteria for quantum-resistant public key cryptography standards. The criteria will include security and performance requirements. The draft criteria will be released for public comments in 2016 and hopefully finalized by the end of the year.
The team accomplished it, in part, by finding a less complicated way to encode and correct the information. The Yale researchers devised a microwave cavity in which they created an even number of photons in a quantum state that stores the qubit. Rather than disturbing the photons by measuring them—or even counting them—the researchers simply determined whether there were an odd or even number of photons. The process relied on a kind of symmetry, via a technique the team developed previously.
"If a photon is lost, there will now be an odd number," said co-lead author Nissim Ofek, a Yale postdoctoral associate. "We can measure the parity, and thus detect error events without perturbing or learning what the encoded quantum bit's value actually is."
A research team from the Quantum Photonics Laboratory at RMIT University and EQuS at the University of Sydney has demonstrated a new technique for quantum tomography—self-guided quantum tomography—which opens future pathways for characterisation of large quantum states and provides robustness against inevitable system noise.
"Self-guided quantum tomography uses a search algorithm to iteratively 'find' the quantum state."