## Pages

### Quantum Computers: A Threat to Blockchain?

How Can a Quantum Computer Pose a Threat?

There are two main concepts behind the quantum computer: superposition and quantum entanglement.

The superposition allows a quantum bit (qbit) to be in several states at the same time, and with the help of quantum entanglement, the observer can find out the parameters of a particle in any position in the universe. The connection is preserved, even if they are moved into different parts of the Universe.

In essence, a quantum computer can process and analyze infinite bits of information at the same time — and so quickly and differently than the human mind cannot grasp it.

### Hybrid qubits solve key hurdle to quantum computing

... In 1998, Daniel Loss, one of the authors of the current study, came up with a proposal, along with David DiVincenzo of IBM, to build a quantum computer by using the spins of electrons embedded in a quantum dot—a small particle that behaves like an atom, but that can be manipulated, so that they are sometimes called "artificial atoms." In the time since then, Loss and his team have endeavored to build practical devices.

... it is based on semiconductors, for which a large industry already exists. ...

### How quantum computers will make 5 unsolvable computing problems disappear.

https://interestingengineering.com/5-intractable-problems-quantum-computing-will-solve

Encryption and Cybersecurity
Financial Services
Drug Research and Development
Supply Chain Logistics
Exponentially Faster Data Analysis

... 90 percent of all data produced in human history was produced within the last two years.
... MIT partnered with Google to mathematically demonstrated the ways in which quantum computers, when paired with supervised machine learning, could achieve exponential increases in the speed of data categorization.

... governments are investing heavily in quantum computer systems research as are major tech titans like Google and IBM. These developments are expected to begin impacting the 5 areas of the economy we looked at within the next decade, and maybe as early as 2020.

### 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," ...

--------------------------

### Tiny camera lens may help link quantum computers to network

... 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

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.

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.

...

### 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

Researchers have experimentally demonstrated two cornerstones of quantum physics—entanglement and Bell inequality violations—with two macroscopic mechanical resonators.
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-$𝜇\text{m}$-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.

### Physicists quantify the usefulness of 'quantum weirdness'

https://phys.org/news/2016-04-physicists-quantify-quantum-weirdness.html

For the past 100 years, physicists have been studying the weird features of quantum physics, and now they're trying to put these features to good use. One prominent example is that quantum superposition (also known as quantum coherence)—which is the property that allows an object to be in two states at the same time—has been identified as a useful resource for quantum communication technologies.

Recently, physicists have been developing ways to measure the amount of quantum coherence in a system. Now in two new papers, a team of physicists and mathematicians (Carmine Napoli, et al., and Marco Piani, et al.) has introduced a way to quantify the usefulness of quantum coherence by looking at this property from a purely operational perspective. The new measurement method can answer questions such as "how useful will a system's quantum coherence be for a task like encoding and decoding secret messages?" In other words, the new method quantifies the advantage of using quantum mechanics.

"We introduce a new way to quantify quantum coherence, the quintessential signature of quantum mechanics, capturing the extent to which a system can live in a superposition of distinct states (like a coin being simultaneously heads and tails, or a famous cat dead and alive)," the researchers wrote.
Spotting nature's own evolution of quantum tricks could transform quantum technology

https://phys.org/news/2018-11-nature-evolution-quantum-technology.html
The Sun Wouldn't Shine Without Quantum Physics

https://www.forbes.com/sites/startswithabang/2018/11/23/the-sun-wouldnt-shine-without-quantum-physics/

Quantum adiabatic and quantum circuit algorithms are equivalent

Algorithms for adiabatic quantum computers were first proposed in 2000 and since then, researchers have shown that quantum adiabatic algorithms and quantum circuit algorithms are “polynomially equivalent”. This means that if one type of algorithm takes time t to solve a problem, then the other will take a polynomial value of t to the nth power to complete the task.

### Universal Quantum Phenomenon Found in Superconductors

https://www.quantamagazine.org/universal-quantum-phenomenon-found-in-superconductors-20181119/

### Breakthrough neural network paves the way for quantum AI

Quantum computers put blockchain security at risk
Bitcoin and other cryptocurrencies will founder unless they integrate quantum technologies
https://www.nature.com/articles/d41586-018-07449-z

---------------------

The environment needs cryptogovernance
https://www.nature.com/news/the-environment-needs-cryptogovernance-1.22023

---------------------

Here’s what the quantum internet has in store
https://www.nature.com/articles/d41586-018-07129-y

---------------------

First quantum computers need smart software
https://www.nature.com/news/first-quantum-computers-need-smart-software-1.22590

---------------------

Commercialize quantum technologies in five years
https://www.nature.com/news/commercialize-quantum-technologies-in-five-years-1.21583

---------------------

Quantum mechanics in fractal geometry

Molecules on a metal surface can sculpt the surface electrons into shapes not found in nature.
https://physicstoday.scitation.org/do/10.1063/PT.6.1.20181119a/full/

---------------------

Error correction in the quantum world

The physicist has a clear goal: he wants to build a quantum computer that is not only powerful, but also works without errors.
https://phys.org/news/2018-11-error-quantum-world.html

------------------------------------------------------------------

The quantum internet has arrived (and it hasn’t)

Quantum teleportation is even weirder than you think

### Niels Bohr's Quantum Mechanics and Philosophy of Physics

When Bohr first published his findings in 1913, Albert Einstein called it “musicality in the sphere of thought.” He would also later go on to say, “If all this is true, then it means the end of physics.” Bohr himself said that "[a]ny one who is not shocked by quantum theory doesn't understand it."
Einstein was not alone in his reservations. Bohr’s protégés and other physicists working from Bohr’s model were proposing truly radical ideas. Heisenberg would go on to show that you could not observe the position of a particle and observe its momentum at the same time. He would also introduce an extensive “matrix mechanics” that could be used to calculate the properties of particles.
Erwin Schrodinger proposed a different theory that an electron was not a particle, but a wavefunction that spread itself through space. To the disbelief of many at the time, it was shown that both Schrodinger and Heisenberg were correct, and that their methods were interchangeable; and by extension that an electron was both particle and wave at the same time.

## Complementarity: A New Philosophy of Physics

One of Bohr’s more controversial and lasting contributions to the debate was his introduction of the concept of Complementarity. Bohr found that if you were to take a measurement of an electron with one apparatus, it would predictably behave like a particle. Make the same measurement with another apparatus and suddenly it behaved like a wave.
Such results would have driven most physicists mad looking for a way to reconcile this contradiction, but Bohr proposed that it was pointless to try. Bohr said that our understanding of light and other quantum phenomena was furthered by measuring it as either particle or wave, but since one could not do both at the same time, the observer must decide how to observe it and accept that doing so foreclosed the possibility of observing it differently.
More radically, he declared that there was no paradox to solve since physics shouldn’t be about the thing being studied, but should be about the results of experiment and observations. In this way, Complementarity challenged much of the philosophy of physics which held fast to the idea that knowable laws governed the universe and everything in it, and that anything in the universe could be defined by a unified set of properties.
By saying that a single thing could have more than one mutually-exclusive definition of equal validity and that we need both definitions to truly understand the thing in question, he touched off a metaphysical controversy in physics that is still being fought today.

## Reaction to Bohr’s Ideas

While he initially welcomed and approved of Bohr’s work, Einstein would go on to become Bohr’s most famous critics, even though they were personally close. Einstein was married to the deterministic view of physics, so the imposition of randomness and uncertainty into the foundation of physics troubled him. Famously, he remarked that "God does not play dice with the universe."
None other than Schrodinger himself added to the criticism when he proposed his most famous thought experiment of a cat in a box in which the radioactive decay of an atom inside triggers the release of cyanide. According to the Quantum Mechanics that he himself help to build, until you opened the box to see if the atom has decayed, the atom exists in both decayed and non-decayed states. If this were true, then Schrodinger’s cat was both alive and dead at the same time.
Originally meant to prove how the new theories were going off the rails, Schrodinger inadvertently confirmed the maddeningly weird nature of Quantum Mechanics, since the superpositions of particles has long been an established fact. The radioactive atom in Schrodinger’s box is in fact decayed and not until it is observed; his cat is both dead and alive until an observer opens the box.
Trying to untangle this and other problems of quantum mechanics has even given rise to new models of reality, such as the theory of the Multiverse. Moreover, the concept of Complementarity is a subject of intense debate not just in the field of physics but also among philosophers, some of whom accuse Bohr of a "simple-minded positivis[m]."
Others carelessly attribute ideas to Bohr that he never expressed. In particular, some critics of Complementarity claim that it means that simply observing a particle changes its behavior to one mutually exclusive state or the other.
Bohr, however, never made such a claim, arguing only that when observing a particle with a specific instrument, the particle will react to that instrument, predictably, as either a wave or a particle and will do so every time. Using another instrument will yield a different result and so the observer's choice of instrument will dictate what behavior they will observe.

## Bohr’s Lasting Legacy

Over the last century, Bohr’s critics waited for some final repudiation of Bohr’s work that never came. Instead, Einstein’s Relativity has been repeatedly confirmed and built upon by later physicists like the late Steven Hawkings.
Meanwhile, Bohr’s discoveries underpin some of the most advanced technology currently being developed. Quantum computers, built entirely off the principles of quantum entanglement that drove Einstein to distraction, promise an unfathomable increase in computing power over classical computers and have already been built by companies such as Google and in University labs all over the world.
Finally, it was Bohr himself who proposed that the complementarity of these different sets of rules allow us to have a fuller understanding of the world we live in. For this and much much more, we will forever remember his genius.

https://interestingengineering.com/niels-bohrs-quantum-mechanics-and-philosophy-of-physics

### Quantum Machine Learning

... Since quantum systems produce counter-intuitive patterns believed not to be efficiently produced by classical systems, it is reasonable to postulate that quantum computers may outperform classical computers on machine learning tasks. The field of quantum machine learning explores how to devise and implement concrete quantum software that offers such advantages. Recent work has made clear that the hardware and software challenges are still considerable but has also opened paths towards solutions.

https://arxiv.org/abs/1611.09347

==============================

23/03/2018
В понедельник, 26 марта в 18:30 в 239 НК, с реферативным докладом по статье J. Biamonte, et al. - Quantum Machine Learning, Nature 549, 195-202 (2017) выступит студентка 2-го курса МФТИ Мусина Лилия.

Аннотация статьи:
Recent progress implies that a crossover between machine learning and quantum information processing benefits both fields. Traditional machine learning has dramatically improved the benchmarking and control of experimental quantum computing systems, including adaptive quantum phase estimation and designing quantum computing gates. On the other hand, quantum mechanics offers tantalizing prospects to enhance machine learning, ranging from reduced computational complexity to improved generalization performance. The most notable examples include quantum enhanced algorithms for principal component analysis, quantum support vector machines, and quantum Boltzmann machines. Progress has been rapid, fostered by demonstrations of midsized quantum optimizers which are predicted to soon outperform their classical counterparts. Further, we are witnessing the emergence of a physical theory pinpointing the fundamental and natural limitations of learning. Here we survey the cutting edge of this merger and list several open problems.

### Quantum computing, not AI, will define our future

... It’s been said that quantum computers will break current encryption schemes, kill blockchain, and serve other dark purposes.
...
If you want to get involved, check out the free tools that the household-name computing giants such as IBM and Google have made available, as well as the open-source offerings out there from giants and start-ups alike. Actual time on a quantum computer is available today, and access opportunities will only expand.
In keeping with my view that proprietary solutions will succumb to open-source, collaborative R&D and universal quantum computing value propositions, allow me to point out that several dozen start-ups in North America alone have jumped into the QC ecosystem along with governments and academia. Names such as Rigetti Computing, D-Wave Systems, 1Qbit Information Technologies, Inc., Quantum Circuits, Inc., QC Ware, Zapata Computing, Inc. may become well-known or they may become subsumed by bigger players, their burn rate – anything is possible in this nascent field.
...

### You Experience the Quantum World Every Time You See, Touch, or Smell

Molecules of very different shapes can all smell the same, and molecules of similar shapes can smell very differently. There must be some other difference that the receptors are picking up on. That difference may lie in quantum physics.

Molecules all have a different vibrational frequency, depending on their mass, their bonds, and their structure. It's possible that our noses detect the differences in vibration between molecules, rather than just their shape. There's some evidence for this: A scientist in the 1990s compared the scents of two molecules with different shapes but identical molecular frequencies and found that they smelled exactly the same.

https://curiosity.com/topics/you-experience-the-quantum-world-every-time-you-see-touch-or-smell-curiosity

### Quantum network to test unhackable communications

https://phys.org/news/2018-10-quantum-network-unhackable.html

"This is the first time anyone has even planned to carry out a quantum network like this: a permanent, functioning quantum teleportation network at long distances in the United States," said Fermilab Deputy Director and Chief Research Officer Joe Lykken. "We want to demonstrate the enabling quantum technology. And we want to capitalize on our expertise to pave the way for others to create their own networks. Decades ago, building something like this would have been just a dream. But we're doing it now, and soon others will be able to."