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Researchers have developed an advanced optical technique to uncover hidden properties of the quantum material Ta2NiSe5 (TNS) using light. By employing terahertz time-domain spectroscopy, the team observed anomalous terahertz light amplification, indicating the presence of an exciton condensate. This discovery opens up new possibilities for using quantum materials in entangled light sources and other applications in quantum physics. Credit: SciTechDaily.com

Scientists used a laser-based technique to reveal hidden quantum properties of the material Ta2NiSe5, potentially advancing the development of quantum light sources.

Certain materials have desirable properties that are hidden, and just as you would use a flashlight to see in the dark, scientists can use light to uncover these properties.

Researchers at the University of California San Diego have used an advanced optical technique to learn more about a quantum material called Ta2NiSe5 (TNS). Their work was published in the journal Nature Materials.

Materials can be perturbed through different external stimuli, often with changes in temperature or pressure; however, because light is the fastest thing in the universe, materials will respond very quickly to optical stimuli, revealing properties that would otherwise remain hidden.

Using an improved technique that gave access to a broader range of frequencies, the team was able to uncover some of the hidden properties of the TNS exciton condensate. Credit: Sheikh Rubaiat Ul Haque / Stanford University

In essence, we shine a laser on a material and its like stop-action photography where we can incrementally follow a certain property of that material, said Professor of Physics Richard Averitt, who led the research and is one of the papers authors. By looking at how constituent particles move around in that system, we can tease out these properties that are really tricky to find otherwise.

The experiment was conducted by lead author Sheikh Rubaiat Ul Haque, who graduated from UC San Diego in 2023 and is now a postdoctoral scholar at Stanford University. He, along with Yuan Zhang, another graduate student in Averitts lab, improved upon a technique called terahertz time-domain spectroscopy. This technique allows scientists to measure a materials properties over a range of frequencies, and Haques improvements allowed them access to a broader range of frequencies.

The work was based on a theory created by another of the papers authors, Eugene Demler, a professor at ETH Zrich. Demler and his graduate student Marios Michael developed the idea that when certain quantum materials are excited by light, they may turn into a medium that amplifies terahertz frequency light. This led Haque and colleagues to look closely into the optical properties of TNS.

When an electron is excited to a higher level by a photon, it leaves behind a hole. If the electron and hole are bound, an exciton is created. Excitons may also form a condensate a state that occurs when particles come together and behave as a single entity.

Haques technique, backed by Demlers theory and using density functional calculations by Angel Rubios group at Max Planck Institute for the Structure and Dynamics of Matter, the team was able to observe anomalous terahertz light amplification, which uncovered some of the hidden properties of the TNS exciton condensate.

Condensates are a well-defined quantum state and using this spectroscopic technique could allow some of their quantum properties to be imprinted onto light. This may have implications in the emerging field of entangled light sources (where multiple light sources have interconnected properties) utilizing quantum materials.

I think its a wide-open area, stated Haque. Demlers theory can be applied to a suite of other materials with nonlinear optical properties. With this technique, we can discover new light-induced phenomena that havent been explored before.

Reference: Terahertz parametric amplification as a reporter of exciton condensate dynamics by Sheikh Rubaiat Ul Haque, Marios H. Michael, Junbo Zhu, Yuan Zhang, Lukas Windgtter, Simone Latini, Joshua P. Wakefield, Gu-Feng Zhang, Jingdi Zhang, Angel Rubio, Joseph G. Checkelsky, Eugene Demler and Richard D. Averitt, 3 January 2024, Nature Materials.DOI: 10.1038/s41563-023-01755-2

Funding provided by the DARPA DRINQS Program (D18AC00014), the Swiss National Science Foundation (200021_212899), Army Research Office (W911NF-21-1-0184), the European Research Council (ERC-2015-AdG694097), the Cluster of Excellence Advanced Imaging of Matter (AIM), Grupos Consolidados (IT1249-19), Deutsche Forschungsgemeinschaft (170620586), and the Flatiron Institute.

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Shadows and Light: Discovering the Hidden Depths of Quantum Materials - SciTechDaily

The morning coffee will swirl with clouds of white liquid if a dash of creamer is added. But after a few seconds, those swirls will go, and it will be left with a regular brown liquid in a mug.

In the current study, Nandkishore and his colleagues used mathematical tools to envision a checkerboard pattern of theoretical qubits. The team discovered that if they arranged these zeros and ones in the right way, the patterns could flow around the checkerboard but might never disappear entirely. Image Credit: Stephen, Hart & Nandkishore

Information can quickly become jumbled in quantum computer chips, which are devices that tap into the strange features of the universe at its smallest scales. This limits the memory capacity of these devices.

That does not have to be the case, notes Rahul Nandkishore, Associate Professor of Physics at CU Boulder.

Using mathematical techniques, he and his colleagues have made a significant breakthrough in theoretical physics by demonstrating that it is possible to construct a situation in which milk and coffee do not mix, regardless of how vigorously they are stirred.

The team's research could result in improved quantum computer chips and give engineers new avenues to store data in minuscule items.

Think of the initial swirling patterns that appear when you add cream to your morning coffee; imagine if these patterns continued to swirl and dance no matter how long you watched.

Rahul Nandkishore, Senior Author and Associate Professor, Department of Physics, University of Colorado Boulder

To confirm that these infinite swirls are indeed feasible, more laboratory tests are required. However, the team's findings represent a significant advancement for physicists working on the project known as "ergodicity breaking," which aims to produce materials that stay out of equilibrium for extended periods of time.

The group's results were published in the journal "Physical Review Letters."

The study's universal issue in quantum computing is what drives co-authors David Stephen and Oliver Hart, postdoctoral physics researchers at CU Boulder.

Typically, "bits," which are represented by zeros or ones, power computers. Contrarily, Nandkishore clarified, quantum computers use "qubits," which are entities that can exist as either zero or one at the same moment due to the peculiarities of quantum mechanics.

Qubits have been created by engineers using a variety of materials, such as single atoms trapped by lasers or small components known as superconductors.

But qubits are readily confused, much like that cup of coffee. For instance, if every qubit is flipped to one, the qubits will ultimately flip back and forth until the chip as a whole becomes a disorganized mess.

In their recent research, Nandkishore and his colleagues may have identified a method to overcome the usual tendency of qubits to mix. The group conducted calculations suggesting that if scientists organize qubits into specific patterns, these configurations would preserve their information even when subjected to disturbances such as a magnetic field.

This finding raises the possibility of constructing devices with a form of quantum memory, according to the physicist.

This could be a way of storing information; you would write information into these patterns, and the information could not be degraded.

Rahul Nandkishore, Senior Author and Associate Professor, Department of Physics, University of Colorado Boulder

In the study, an array of hundreds to thousands of qubits arranged in a checkerboard-like pattern was seen by the researchers using mathematical modeling techniques.

They found that packing the qubits into a small space was the key. According to Nandkishore, qubits can affect the actions of their neighbors if they are near enough to one another. It is similar to a throng of people attempting to cram themselves into a phone booth. Even if some of those individuals are either standing straight or on their heads, they are unable to turn around without shoving into other people.

According to their calculations, if these patterns were formed precisely, they may flow around a quantum computing chip and never break down, much like the clouds of cream that swirl indefinitely throughout the coffee.

Nandkishore said, The wonderful thing about this study is that we discovered that we could understand this fundamental phenomenon through what is almost simple geometry.

The teams findings could influence a lot more than just quantum computers.

However, his recent discoveries add to the increasing amount of evidence that implies certain small matter organizations can resist that equilibrium, thereby defying some of the universe's most inflexible laws.

According to Nandkishore, nearly everything in the universe, from massive seas to coffee cups, tends to gravitate toward a state known as "thermal equilibrium." When you place an ice cube inside the mug, for instance, the heat from the coffee will cause the ice to melt and finally turn into a liquid that is all the same temperature.

We are not going to have to redo our math for ice and water. The field of mathematics that we call statistical physics is incredibly successful in describing things we encounter in everyday life. But there are settings where maybe it does not apply.

Rahul Nandkishore, Senior Author and Associate Professor, Department of Physics, University of Colorado Boulder

Stephen, D. T., et.al., (2024). Ergodicity Breaking Provably Robust to Arbitrary Perturbations. Physical Review Letters. doi.org/10.1103/physrevlett.132.040401

Source: https://www.colorado.edu/

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The Science Behind the Swirling Patterns in Your Morning Coffee - AZoQuantum

Quantum Key Distribution (QKD) is a method of secure communication that uses principles of quantum mechanics to enable two parties to produce a shared random secret key. This key can then be used to encrypt and decrypt messages, providing a secure means of communication.

The fundamental idea behind QKD is based on the principles of quantum superposition and entanglement. In traditional cryptographic systems, the security of the communication relies on mathematical algorithms, whereas QKD leverages the unique properties of quantum particles to achieve its security.

Heres a basic overview of how Quantum Key Distribution (QKD) works:

In quantum mechanics, particles like photons can exist in multiple states at once(superposition). In the context of QKD, a sender (Alice) can encode information in the quantum states of particles (e.g., photons) and send them to the receiver (Bob).

2. Quantum Entanglement:

Entanglement is a quantum phenomenon where particles become correlated in such a way that the state of one particle is directly related to the state of another, regardless of the distance between them. This property is used in some QKD protocols to ensure the security of the key exchange.

3. Measurement:

When Bob receives the quantum states from Alice, he performs measurements on these particles. The act of measurement, according to quantum mechanics, changes the state of the particles. Bob communicates the outcomes of his measurements to Alice over a classical communication channel.

4. Key Generation:

Alice and Bob compare a subset of their measurement outcomes to check for discrepancies. If an eavesdropper (an unauthorized third party) tries to intercept or measure quantum states, the act of measurement will disturb the quantum states, and Alice and Bob will notice inconsistencies.

5. Error Correction and Privacy Amplification:

If they detect any discrepancies, Alice and Bob can discard those bits and perform error correction to generate a final secret key. Additionally, privacy amplification techniques are used to enhance the security of the key.

One of the key advantages of QKD is its ability to provide information-theoretic security, meaning that the security is based on the fundamental laws of physics and not on computational assumptions. However, its important to note that while QKD offers a highly secure method for key distribution, it doesnt address all aspects of secure communication, and additional classical cryptographic protocols are often used in conjunction with QKD to achieve comprehensive security.

References: The information is summarised from multiple online resources.

Previous articles:

Why Quantum Computing matters and what do you need to know?

What is Quantum Computing?

Unleashing the Power: When Quantum Computing and AI Join FOrces to Shape Tomorrows World

Navigating the Quantum Revolution: A Closer Look at Cryptographys Future

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What is Quantum Key Distribution? | by Sai Nitesh | Jan, 2024 - Medium

String theory works only in a 10-dimensional model. MEDHA SURAJPAL/THE VARSITY

What string theory says about existence in other dimensions

Youve probably wondered at some point what life would be like in different dimensions. I certainly have.

Living in the first dimension would consist of us existing as points on a line. This dimension can be visualized as an infinite line or equated to the x-axis on a graph. We would have no concept of size, and any object would always appear as a point with no depth or breadth.

If we add another axis to this dimension, namely the y-axis, that would establish flat land or two-dimensional (2D) space. Here, we could exist as shapes and perceive other shapes around us. Notably, as flatlanders, we would view other objects from the side as lines with no depth existing on the same flat plane.

In actuality, we exist in the third dimension (3D). As 3D creatures, we can view the 2D plane from the top and see what a rectangle and other 2D objects fully look like. However, despite living in a 3D world, our eyes process visual information in 2D, which our brain supports with depth cues so that we can still perceive the three-dimensional things around us.

In this pattern, we could keep going to a higher dimension, where a creature in each dimension would process the world in a dimension lower than the one in which it exists and then use depth cues to perceive its own dimension.

In practice sadly physicists havent really found much evidence of spatial dimensions beyond the usual three, plus a fourth dimension of time. However, one prevalent theory that has gotten the closest to being a viable candidate for the Theory of Everything a grand theory that aims to unify the fundamental forces of physics which posits that the universe has nine spatial dimensions and one dimension of time. This theory is called string theory.

String theory

String theory arose as an attempt to unify quantum mechanics and general relativity. The former studies and describes the movement and interactions of subatomic particles while the latter is Albert Einsteins theory of how gravity affects space-time, the fabric of the universe that distorts under the movement of massive objects.

Together, these theories describe the four fundamental forces that govern interactions in the universe: the strong force, the weak force, the electromagnetic force, and gravity. The first three are described by quantum mechanics, and the last one is described by general relativity.

However, applying Einsteins idea of general relativity to quantum systems just yields nonsensical mathematical solutions. Since larger objects are made up of subatomic particles, using completely disconnected systems to describe the behaviour of subatomic particles and the behaviour of larger objects seems illogical. A Theory of Everything aims to bridge this gap.

In 1984, two physicists, John Schwarz and Michael Green, suggested the beginnings of string theory, which would ease the mathematical antagonism between general relativity and quantum mechanics.

Traditionally, physicists have seen natures fundamental particles as the neutrons, protons, and electrons that make up atoms, which in turn make up everything. Neutrons and protons can be broken down even further into quarks.

String theory further breaks down these fundamental particles and posits that all particles are made of minuscule strings of energy vibrating at different frequencies. The theory unifies the fundamental forces by having all particles be made of the same underlying basic component of strings.

The three fundamental forces governed by quantum mechanics can be quantized to discrete particles: the strong nuclear force is carried and transferred by the gluon, the weak nuclear force by W and Z bosons, and the electromagnetic force by the photon.

However, a hypothetical particle that transmits gravity called the graviton is incompatible under a quantum mechanics framework like the other forces are.

Interestingly, under the paradigm of string theory, a graviton is associated with a string frequency. Similarly, there is an associated string frequency for gluons, W and Z bosons, and photons, uniting gravity with quantum mechanics by describing them under the same framework.

Dimensions in string theory

The math for string theory that unifies these particles does not work in our current four-dimensional model. In fact, it only works in 10 dimensions, one of which is time. The actual view we would have of each dimension is also different from the previous progression we explored from 1D to 3D worlds.

String theory postulates two basic types of dimensions: those that are very large and expanded and those that are really small and wound up. Large dimensions are those that we can experience.

Brian Greene, a physicist specializing in the study of string theory, compares a large dimension to a wide carpet and a small dimension to the wound-up circular loops that make up the carpet that you have to bend down to see. In other words, we may have three dimensions we can experience and easily navigate and six other spatial dimensions that might be so tightly wound up that we simply cant perceive them.

Unfortunately, there has been no substantial experimental support for string theory thus far. That doesnt mean that string theory has no basis, though. It results from decades of analysis and intense study and is the closest physicists have ever come to the Theory of Everything. String theory has truly been significant in expanding our understanding of reality.

And who knows? Maybe someday, we will have evidence for string theory and multiple dimensions. Until then, its certainly fun imagining them.

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What if there were more than three dimensions? - Varsity