New optical device brings quantum computing a step closer

https://phys.org/news/2018-12-optical-device-quantum-closer.html

The microchip - which is 1.5cm wide, 5cm long and 0.5cm thick - has components inside that interact with light in different ways. These components are connected by tiny channels called waveguides that guide the light around the microchip, in a similar way that wires connect different parts of an electric circuit.

... "This experiment is the first to integrate three of the basic steps needed for an optical quantum computer, which are the generation of quantum states of light, their manipulation in a fast and reconfigurable way, and their detection," ...

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Tiny camera lens may help link quantum computers to network

https://phys.org/news/2018-09-tiny-camera-lens-link-quantum.html

... Associate Professor Andrey Sukhorukov said the metasurface camera lens was highly transparent, thereby enabling efficient transmission and detection of information encoded in quantum light.

"It is the first of its kind to image several quantum particles of light at once, enabling the observation of their spooky behaviour with ultra-sensitive cameras," said Associate Professor Sukhorukov, who led the research with a team of scientists at the Nonlinear Physics Centre of the ANU Research School of Physics and Engineering.


The unconventional lens, which is 100 times thinner than a human hair, could enable a fast and reliable transfer of quantum information from the new-age computers to a network, once these technologies are fully realised.

The device is made of a silicon film with millions of nano-structures forming a metasurface, which can control light with functionalities outperforming traditional systems.

Researchers demonstrate new building block in quantum computing

December 4, 2018 by Laurie Varma, US Department of Energy

... two entangled photons contained in a single strand of fiber-optic cable—is the "smallest quantum computer you can imagine. This paper marks the first demonstration of our frequency-based approach to universal quantum computing."

"A lot of researchers are talking about quantum information processing with photons, and even using frequency," said Lukens. "But no one had thought about sending multiple photons through the same fiber-optic strand, in the same space, and operating on them differently."

The team's quantum frequency processor allowed them to manipulate the frequency of photons to bring about superposition, a state that enables quantum operations and computing.

...

https://phys.org/news/2018-12-block-quantum.html

About Quantum Computing

https://www.linkedin.com/pulse/20-amazing-facts-quantum-computing-everyone-should-read-bernard-marr

Bernard Marr

...

Quantum mechanics.

1. Quantum computing aims to take advantage of unusual properties that matter exhibits once we begin to study it at a level of detail below atomic level – the sub-atomic, or quantum level.

2. While conventional computer use binary “bits” (one and zero) as the process for calculation, a quantum computer uses quantum bits, knows as qubits – which can exist in both states simultaneously, as well as many other states in between.

3. Qubits exhibit properties of quantum entanglement – a phenomenon that means pairs, or groups, of particles cannot be measured or described independently of each other – they are “entangled” and their state depends on that of other particles in the group.

4. Due to factors which are still not fully understood despite the best efforts of Einstein, Shrodinger and many others since, it appears that particles linked in this way can transfer information between each other, even though, theoretically, they could be an unlimited distance apart.

5. Computer scientists working on quantum computers believe that in the future it will be possible to harness these mechanisms and build computers which will be millions of times more efficient that anything available today.

Meanwhile, in the real-world …

6. The possibility of quantum computing was first proposed by physicist Richard Feynman in 1982.

7. In 1994, mathematician Peter Shaw demonstrated how quantum computing could be used to crack the common encryption standards available then – many of which are still in use today.

8. DARPA brought online the world’s first operational quantum network in 2003, breaking new ground in the fields of quantum computing as well as secure communications.

9. The world’s first dedicated quantum computing focused commercial business – 1Qbit– was established in Vancouver, British Columbia, in 2012.

10. IBM launched Q, which offers 5 qubit quantum computing services via cloud in 2016. Last year it upgraded to 20 qubits of quantum processing power.

11. Organizations which are publicly known to be making use of D-Wave’s quantum computing infrastructure include Google, NASA and Lockheed Martin.

Advocates

12. Satya Nadella, Microsoft CEO: “The world is running out of computing capacity. Moore’s law is kinda running out of steam … [we need quantum computing to] create all of these rich experiences we talk about, all of this artificial intelligence.”

13. Seth Lloyd, author of Programming the Universe: “A classical computation is like a solo voice – one line of pure tones succeeding each other. A quantum computation is like a symphony – many lines of tones interfering with each other.”

14. David Deutsche, Physicist at the Centre for Quantum Computation, Oxford University: “Quantum computation will be the first technology that allows useful tasks to be performed in collaboration between parallel universes.”

15. Jeremy O’Brien, physicist and professorial research fellow at the University of Bristol: “In less than 10 years quantum computers will begin to outperform everyday computers, leading to breakthroughs in artificial intelligence, the discovery of new pharmaceuticals and beyond. The very fast computing power given by quantum computers has the potential to disrupt traditional businesses and challenge our cyber security.”

16. Geordie Rose, CTO at D-Wave: By 2028 intelligent machines will exist that can do anything humans can do. Quantum computers will have played a critical role in the creation of this new type of intelligence.

Mind-Bending Quantum Facts

17. Quantum computing requires extremely cold temperatures, as sub-atomic particles must be as close as possible to a stationary state to be measured. The cores of D-Wave quantum computers operate at -460 degrees f, or -273 degrees c, which is 0.02 degrees away from absolute zero.

18. Quantum computing is often described as “natural”. This is because although we don’t completely understand them, the mechanisms underpinning the real world (which have evolved through nature) clearly operate at a sub-atomic level. By simulating this with computers, we come a huge step closer to being able to simulate the natural world.

19. At a quantum level, science fiction appears to become reality. Particles can travel backwards or forwards in time and teleport (quantum tunnelling) between two positions.

One possible explanation for why quantum computers work involves parallel universes. It has been theorized that qubits are able to exist in two states simultaneously because we are observing them in multiple universes simultaneously.

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Qubits in Q#

https://blogs.msdn.microsoft.com/visualstudio/2018/12/01/qubits-in-qsharp/
December 1, 2018 by Mariia Mykhailova // 1 Comments


How should qubits be represented in a quantum programming language?

In the quantum circuit model, a quantum computation is represented as a sequence of operations, sometimes known as gates, applied to a set of qubits. This leads to pictures such as:

from Quantum Computation and Quantum Information by Nielsen and Chuang

In this picture, each horizontal line is a qubit, each box is an operation, and time flows from left to right.

When we want to design a programming language to express a quantum computation, the question naturally arises of whether qubits should be represented in the language, and if so, how. In the most naive model of such a picture, there would be a software entity that represented each horizontal line, with little or no accessible state other than perhaps a label, but there are other possibilities.

Quantum States as Linear Types

Quipper uses linear types to model quantum states, although it refers to the data type as Qubit. The intuition is that the no-cloning theoremprevents you from making a copy of the quantum state of a qubit, so it makes sense to use the type system to prevent you from making a copy of the software representation of quantum state. Linear types have proven useful in other contexts where copying the software representation of an entity would be bad, for instance in functional concurrent programming, so why not for quantum computing?

The argument for linear types is, as mentioned, that they reflect the no-cloning theorem in the language. The implication is that a software qubit represents a qubit state, rather than an actual object. The problem with this view is that, once entangled, it no longer makes sense to talk about the state of an individual qubit; that’s more or less exactly what being entangled means. To model this in software, an entangling gate such as a CNOT should take two single-qubit states as inputs and return a software entity that represents two-qubit state as output — as long as you never want to perform a CNOT on two qubits that are each entangled with other qubits.

The software entity as quantum state abstraction breaks down for two reasons:

• because quantum computing works by applying operations to physical entities, not to quantum states, so the abstraction doesn’t correspond to operational reality; and
• because in general there is no actual physical quantum state smaller than the state of the entire quantum computer, so the abstraction doesn’t correspond to physical reality.

Qubits as Opaque References

An alternate approach is to use an opaque data type that represents a reference to a specific two-state quantum system, whether physical or logical (error-corrected), on which operations such as `H` or `X` may be performed. This is an operational view of qubits: qubits are defined by what you can do to them. Both OpenQASM and Q# follow this model.

Quantum Computing is Computing by Side Effect

The representation used in Q# has the interesting implication that all of the actual quantum computing is done by side effect. There is no way to directly interact with the quantum state of the computer; it has no software representation at all. Instead, one performs operations on qubit entities that have the side effect of modifying the quantum state. Effectively, the quantum state of the computer is an opaque global variable that is inaccessible except through a small set of accessor primitives (measurements) — and even these accessors have side effects on the quantum state, and so are really “mutators with results” rather than true accessors.

In general programming, the use of side effects and global state is generally discouraged. For quantum computing, on the other hand, they seem to match the actual physical reality pretty well. For this reason, we decided that this abstraction was the right one to use in Q#.

This post is the first one in the Q# Advent Calendar 2018. Follow the calendar for other great posts!

Alan Geller, Software Architect, Quantum Software and Applications
@ageller

Alan Geller is a software architect in the Quantum Architectures and Computation group at Microsoft. He is responsible for the overall software architecture for Q# and the Microsoft Quantum Development Kit, as well as other aspects of the Microsoft Quantum software program.

Physics - Synopsis: Quantum Entanglement With 10 Billion Atoms

https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.121.220404

November 29, 2018

Researchers have experimentally demonstrated two cornerstones of quantum physics—entanglement and Bell inequality violations—with two macroscopic mechanical resonators.

A. Wallucks/Delft University of Technology

While certain quantum behaviors are currently limited to atomic systems, researchers keep searching for hints of quantum physics in more massive objects. Now Simon Gröblacher, of Delft University of Technology in the Netherlands, and colleagues have pushed the boundaries of quantum weirdness to macroscopic scales. They demonstrated quantum entanglement and violations of Bell’s inequality—a canonical test of the principle that all influences on a particle are local and that particle states exist independently of the observer. They used two mechanical resonators, each containing roughly 10 billion atoms.

In their experiments, the team placed two 10-μm$𝜇\text{m}$-long resonators, made of strips of silicon, 20 cm apart in separate arms of an optical interferometer. A laser pulse shot through a beam splitter mechanically excited one of the two resonators, but there was no way to tell which one. The excited resonator emitted a photon, which passed through a second beam splitter and registered at one of two detectors. The emission of this photon signaled entanglement of the mechanical states of the two resonators. A second laser pulse verified the entanglement by converting the excited resonator’s excitation into a second photon, which was also recorded by the detectors.

In April, the team successfully demonstrated their technique, confirming that they could indeed entangle two microscopic resonators. Now, they’ve investigated the entanglement of the two mechanical oscillators with the photons by tracking which of the two detectors registered each of the photons. By measuring correlations between the final destinations of the photons, the team showed that the entanglement of the two resonators and the two photons violates Bell’s inequality by 4 standard deviations.

The team hopes to test quantum mechanics on an even larger scale by creating more complex quantum states of optomechanical systems. Also, by improving the lifetime of the mechanical excitations of the resonators—currently limited to just a few microseconds—the team says that this setup could operate as a memory node in a quantum network.

This research is published in Physical Review Letters.

–Christopher Crockett

Christopher Crockett is a freelance writer based in Arlington, Virginia.