How difficult is it to conquer the quantum nature of matter?

How difficult is it to conquer the quantum nature of matter?


Matt Trusheim includes a switch in a dark laboratory, and powerful green laser illuminates a tiny diamond, held in place under the lens of a microscope. On the computer screen appears an image of a diffuse gas cloud dotted with bright green spots. These spots — tiny defects inside the diamond, in which two carbon atoms replaced by one atom of tin. The laser light, passing through them, passes from one shade of green to another.

Later, the diamond is cooled to the temperature of liquid helium. Controlling the crystalline structure of the diamond atom by atom, bringing it to a few degrees above absolute zero and applying a magnetic field, the researchers from the Laboratory of Photonics of quantum physics under the guidance of Dirk Englund at mit think that they can with such accuracy to select the quantum mechanical properties of photons and electrons that they will be able to pass uncrackable secret codes.

Trusheim — one of many scientists who are trying to figure out which atoms are enclosed in the crystals, under what conditions will allow them to control this level. In fact, scientists worldwide are trying to learn how to control nature at the level of atoms and below, to electrons, or even a fraction of an electron. Their goal is to find the nodes that control the fundamental properties of matter and energy, and tighten or unravel those knots, changing matter and energy to create a heavy duty quantum computers or superconductors that work at room temperature.

These scientists are faced with two main problems. At the technical level to carry out such work is very difficult. Some crystals, for example, must be 99,99999999% pure in vacuum chambers cleaner space. A still more fundamental problem is that quantum effects, which want to rein in scientists — for example, the ability of a particle to be in two States at the same time, like Schrodinger’s cat — are manifested at the level of individual electrons. In the macrocosm, the magic collapses. Therefore, scientists have to manipulate matter at the smallest scales and they are limited by the limits of fundamental physics. Their success depends on how it will change our understanding of the science and technological capabilities in the coming decades.

Alchemist’s dream

The manipulation of a substance to a certain extent, is to control the electrons. In the end, the behavior of electrons in a substance determines its properties as a whole — is this substance a metal, a conductor, a magnet, or something else. Some scientists are trying to change the collective behavior of electrons, creating a quantum synthetic substance. Scientists see how “we take the insulator and turn it into a metal or semiconductor, and then in the superconductor. We can turn non-magnetic material in a magnetic” says scientist Eva Andrei from Rutgers University. “The dream alchemist”.

And this dream can lead to real breakthroughs. For example, scientists for decades have tried to create superconductors that work at room temperature. Using these materials could create the lines, not losing energy. In 1957, physicists John Bardeen, Leon Cooper and John Robert Shiffer demonstrated that superconductivity appears when electrons in metal like aluminium even in so-called Cooper pairs. Even being relatively far away, each to match the other electron having opposite spin and momentum. Like couples dancing in the crowd at the disco, the paired electrons move in coordination with others, even if other electrons are between them.

This alignment allows current to flow through the material without resistance, and hence without loss. Most practical superconductors developed to date should be at a temperature slightly above absolute zero to this state was preserved. However, exceptions can be.

Recently, the researchers found that obstrelivanii material high intensity laser can also capture electrons in a Cooper pair, albeit briefly. Andrea Cavalleri from the Institute for structure and dynamics of matter at the max Planck in Hamburg, Germany, and his colleagues found signs of photoinduced superconductivity in metals and insulators. The light striking the material causes the atoms to vibrate, and the electron briefly enters a state of superconductivity. “Shake-up should be fierce,” says David ESI, the physicist of the condensed substances at Caltech, which uses the same laser technology for the manifestation of unusual quantum effects in other materials. “For a moment the electric field becomes very strong — but only for a short time.”

Uncrackable codes

The management of electrons — that’s how Trusheim and Englund intend to develop uncrackable quantum encryption. In their case the purpose is not to change the properties of the materials, but to transfer quantum properties of electrons in designer diamonds photons, which transmit the cryptographic keys. In the color centers of diamonds in the laboratory Englund located free electrons, spins which can be measured using a strong magnetic field. Spin, which is aligned with the field, can be called a spin-1 spin, which is not aligned, the spin — 2 that will be equivalent to 1 and 0 in digital bit. “It’s a quantum particle, so it can be in both States simultaneously,” says Englund. The quantum bit, or qubit, is able to perform multiple calculations simultaneously.

It is here that is born of the riddle of quantum entanglement. Imagine a box containing red and blue balls. You can take one without looking and put it in his pocket, and then go to another city. Then remove the bulb from the pocket and discover that it is red. You’ll know what’s in the box left blue ball. This is the confusion. In the quantum world, this effect allows you to transmit information instantaneously and over long distances.

Color centers in diamond in the laboratory Englund transmit the quantum state of the electrons enclosed in them, the photons by means of entanglement, creating the “flying qubits” as they call Englund. In ordinary optical communications, the photon can be transferred to the recipient — in this case, the other vacant void in diamond and its quantum state will be transferred to the new electron, so two electrons will be bound. The transfer of such intricate bits would allow two people to share a cryptographic key. “Everyone has a string of zeros and ones, or upper and lower spins, which seem completely random, but they are identical,” says Englund. Using this key to encrypt transmitted data, it is possible to make them absolutely secure. If someone wants to intercept the transmission, the sender will know about it, because the act of measuring a quantum state will change it.

Englund experimenting with the quantum network, which sends the photons via optical fiber through his lab, the facility down the road from Harvard University and another lab at mit in the neighboring town of Lexington. Scientists have already succeeded in the transmission of quantum cryptographic keys over long distances — in 2017, Chinese scientists announced that they gave such a key of the satellite in Earth’s orbit at two ground stations 1200 miles away from each other in the mountains of Tibet. But the bitrate of the Chinese experiment was too low for practical communications: scientists have recorded only one confusing a few of the six million. The innovation that will make a quantum cryptographic network for earth practical is quantum repeaters, devices that are positioned at intervals in the network, which amplify the signal without changing its quantum properties. Englund goal is to find materials with suitable atomic defects to be able to create these quantum repeaters.

The trick is to create enough of entangled photons to transfer data. Electron in attonement jobs maintains its spin long enough — about a second — which increases the chances that the laser light will pass through it and produce a tangled photon. But the nitrogen atom is small and does not fill the space created by the absence of carbon. Therefore, coherent photons can be different colors slightly, and therefore lose the match. Other atoms, tin, for example, adhere firmly to, and create a stable wavelength. But they can’t keep the spin long enough — hence, working to perfect balance.

Split ends

While Englund and others are trying to cope with individual electrons, while others dive deeper into the quantum world and trying to manipulate already shares electrons. This work is rooted in an experiment in 1982, when scientists from bell Labs and National laboratory Lawrence Livermore made a sandwich of two layers of different semiconductor crystals, cooled them almost to absolute zero and applied them to a strong magnetic field, encasing the electrons in the plane between the two layers of crystals. It formed a kind of quantum soup in which the motion of any individual electron is determined by the charges, which he felt from the other electrons. “It is not the individual particles themselves,” says Michael Manfra from Purdue University. “Imagine a ballet in which each dancer not only makes their own PA, but also responds to movement of a partner or other dancers. This is sort of a General response.”

Strange in all this is that such collection can be fractional charges. The electron is an indivisible unit, it will not cut into three pieces, but the group of electrons in the right condition can produce the so-called quasi-particle with 1/3 charge. “If electrons are divided into parts,” says Mohammed Hafezi, a physicist from the Joint Quantum Institute. “It’s very strange.” Hafezi created this effect in sverigeleden graphene, a monoatomic layer of carbon, and recently showed that he can manipulate the movement of quasiparticles, illuminating graphene with a laser. “Now it’s controlled,” he says. “External nodules, such as magnetic field and light can be manipulated to pull or dissolve. Changing the collective nature of change”.

The manipulation of the quasiparticles allow you to create special type of qubit and topological qubit. Topology is a field of mathematics that studies the properties of an object that do not change even if the object is twisted or deformed. The standard example is the donut: if it were perfectly elastic, it could be redefined in a coffee Cup, nothing really changing; the hole in the donut will play a new role in the hole in the handle of the Cup. However, to turn a donut into a pretzel will have to add new holes, changing its topology.

Topological qubit maintains its properties even under varying conditions. Typically, the particles change their quantum state, or “decoherent” when a violation of something in their environment such as small vibrations caused by heat. But if you make a qubit out of two quasi-particles, separated by some distance, say, at opposite ends of the nanowires, you basically laminate the electron. Both “halves” will have to experience the same violation to decoderesult, and this is unlikely that will happen.

This property makes topological qubits are attractive for quantum computers. Because of the ability of a qubit to be in a superposition of multiple States simultaneously, quantum computers should be capable of producing virtually impossible without them calculate, for example, to simulate the Big Bang. Mantra, in fact, trying to create quantum computers of the topological qubits in Microsoft. But there are more simple approaches. Google and IBM, in fact, trying to create quantum computers on the basis of supercooled wires that become semiconductors or ionized atoms in a vacuum chamber held lasers. The problem with these approaches is that they are more sensitive to environmental changes than topological qubits, especially if the number of qubits grows.

Thus, the topological qubit can lead to a revolution in our ability to manipulate tiny things. However, there is one significant problem: they do not yet exist. Researchers are struggling to create them from the so-called Majorana particles. Proposed Ettore Majorana in 1937, this particle is its own antiparticle. Electron and its antiparticle, the positron have identical properties except for charge, but the charge of a Majorana particle is zero.

Scientists believe that certain configurations of electrons and holes (absence of electrons) can behave as Majorana particles. They, in turn, can be used as topological qubits. In 2012, physicist Leo Kouwenhoven from the Technological University of Delft in the Netherlands and his colleagues measured what seemed to them to be Majorana particles in a network of superconducting and semiconducting nanowires. But the only way to prove to exist these quasiparticles will be to create a topological qubit based on them.

Other experts in this field are more optimistic. “I think that without any issues one day someone will create a topological qubit, just for fun,” says Steve Simon, a theorist of condensed materials at Oxford University. “The only question is whether we will be able to make them quantum computer of the future.”

Quantum computers — as well as high-temperature superconductors and uncrackable quantum encryption — can occur after many years or not appear never. But at the same time, scientists are trying to decipher the mysteries of nature at the smallest scales. While no one knows how far they’ll be able to go. The deeper we penetrate into the smallest components of our Universe, the more they have pushed.