Login with your Social Account

A new quantum measurement protocol

Researchers develop new measurement protocol for quantum particles

A new protocol for measurement developed at TU Wien will help in the measurement of the quantum phase of electrons. This is a significant step in attosecond physics. The work appears in the Physical Review Letters.

The current methods in attosecond physics help to measure very short intervals of time. We can track physical processes with very high precision, attoseconds to be precise which is equal to billionths of a billionth of a second.

This can be done using short laser pulses. The ionisation of one atom can be studied along with the process in which an electron exits the atom. Electrons do not always display the particle properties since the quantum-physical wave behaviour plays a major role. It is a wave oscillating in a very short time scale. The task to measure the cycle duration of such oscillations is challenging, however, it is even more difficult to measure the phase. Questions such as how would the electron waves oscillate if an electron can be ionized in two ways get quite tricky. 

A group of researchers from TU Wien and CREOL College, University of Central Florida has developed a protocol for measuring the phase of the electron waves. This can help in understanding photovoltaics in a better manner. 

Stefan Donsa, a team member working under Prof. Joachim Burgdörfer, Institute for Theoretical Physics, TU Wien mentioned that a wave consists of crests and troughs. Its phase tells the location of these points in space and time. Perfect overlapping of quantum waves, such that every wave peak meets a wave peek of other one adds up the waves, on the other hand, if the crest superimposes with the trough then they get cancelled. Hence phase shifts are very important in quantum physics. For this, a reference clock is needed that can make sure the overlap occurs at the exact time without any shift. The latest measurement protocol uses an atomic process as a reference for the other one. 

Helium atoms have been studied in computer simulations where a photon absorption results in emission of an electron. This ejected electron has a certain phase that is difficult to measure. The trick of the new method is to add a second quantum effect serving as a clock, i.e. a quantum metronome. The atom can absorb two photons instead of one under specific conditions. It leads to the same event, an electron emitted with particular energy but this can be measured as it has a different phase. Complicated protocols are needed in attosecond physics. Although there are many such protocols, none allows for the direct measurement of the phase of electron. 

Stefan Donsa said that this measurement protocol allows for the translation of information about an electron phase to its spatial distribution by a combination of special laser pulses. The right laser pulses can help in getting the phase information from the electron’s angular distribution. 

The protocols have to be experimented now to identify which quantum mechanical information can actually be obtained. 

Journal Reference: Physical Review Letters.

Strange warping geometry helps to push scientific boundaries

Strange warping geometry helps to push scientific boundaries

Researchers led by Andrew Houck, a professor of electrical engineering, have built an electronic array on a microchip that simulates particle interactions in a hyperbolic plane, a geometric surface in which space curves away from itself at every point. A hyperbolic plane is difficult to envision — the artist M.C. Escher used hyperbolic geometry in many of his mind-bending pieces — but it is perfect for answering questions about particle interactions and other challenging mathematical questions.

The research team used superconducting circuits to create a lattice that functions as a hyperbolic space. When the researchers introduce photons into the lattice, they can answer a wide range of difficult questions by observing the photons’ interactions in the simulated hyperbolic space.

Geometric pattern

Princeton researchers have built an electronic array on a microchip that simulates particle interactions in a hyperbolic plane, a geometric surface in which space curves away from itself at every point. Image courtesy of the researchers

“You can throw particles together, turn on a very controlled amount of interaction between them, and see the complexity emerge,” said Houck, who was the senior author of the paper published July 4 in the journal Nature.

Alicia Kollár, a postdoctoral research associate at the Princeton Center for Complex Materials and the study’s lead author, said the goal is to allow researchers to address complex questions about quantum interactions, which govern the behavior of atomic and subatomic particles.

“The problem is that if you want to study a very complicated quantum mechanical material, then that computer modeling is very difficult. We’re trying to implement a model at the hardware level so that nature does the hard part of the computation for you,” she said.

The centimeter-sized chip is etched with a circuit of superconducting resonators that provide paths for microwave photons to move and interact. The resonators on the chip are arranged in a lattice pattern of heptagons, or seven-sided polygons. The structure exists on a flat plane, but simulates the unusual geometry of a hyperbolic plane.

“In normal 3-D space, a hyperbolic surface doesn’t exist,” said Houck. “This material allows us to start to think about mixing quantum mechanics and curved space in a lab setting.”

Trying to force a three-dimensional sphere onto a two-dimensional plane reveals that space on a spherical plane is smaller than on a flat plane. This is why the shapes of countries appear stretched out when drawn on a flat map of the spherical Earth. In contrast, a hyperbolic plane would need to be compressed in order to fit onto a flat plane.

“It’s a space that you can mathematically write down, but it’s very difficult to visualize because it’s too big to fit in our space,” explained Kollár.

To simulate the effect of compressing hyperbolic space onto a flat surface, the researchers used a special type of resonator called a coplanar waveguide resonator. When microwave photons pass through this resonator, they behave in the same way whether their path is straight or meandering. The meandering structure of the resonators offers flexibility to “squish and scrunch” the sides of the heptagons to create a flat tiling pattern, Kollár said.

A schematic of the resonators on the microchip, which are arranged in a lattice pattern of heptagons, or seven-sided polygons. The structure exists on a flat plane, but simulates the unusual geometry of a hyperbolic plane.

Courtesy of the researchers

Looking at the chip’s central heptagon is akin to looking through a fisheye camera lens, in which objects at the edge of the field of view appear smaller than in the center: the heptagons look smaller the farther they are from the center. This arrangement allows microwave photons that move through the resonator circuit to behave like particles in a hyperbolic space.

Geometric pattern

A schematic of the resonators on the microchip, which are arranged in a lattice pattern of heptagons, or seven-sided polygons. The structure exists on a flat plane but simulates the unusual geometry of a hyperbolic plane. Courtesy of the researchers

The chip’s ability to simulate curved space could enable new investigations in quantum mechanics, including properties of energy and matter in the warped space-time around black holes. The material could also be useful for understanding complex webs of relationships in mathematical graph theory and communication networks. Kollár noted that this research could eventually aid the design of new materials.

But first, Kollár and her colleagues will need to further develop the photonic material, both by continuing to examine its mathematical basis and by introducing elements that enable photons in the circuit to interact.

“By themselves, microwave photons don’t interact with each other — they pass right through,” she said. Most applications of the material would require “doing something to make it so that they can tell there’s another photon there.”

Kollár plans to continue this line of research as she begins a faculty position at the University of Maryland this summer. Mattias Fitzpatrick, who received a Ph.D. in electrical engineering on June 4, co-authored the study along with Kollár and Houck. On Aug. 15, Fitzpatrick will begin a postdoctoral fellowship with Nathalie de Leon, an assistant professor of electrical engineering at Princeton.

Reference: Hyperbolic lattices in circuit quantum electrodynamics

Materials provided by Princeton University

5CB Liquid Crystal

Scientists manufacture on demand designer atoms

In the near future, scientists may be able to create customised atoms as per one’s requirements with only a button’s click. It may sound like science fiction now but a team of researchers at the University of Colorado Boulder reported that they are slowly approaching the possibility of controlling and assembling particles known as “big atoms”.

The research has been published in the Nature journal. It is centred around the colloidal particles which after mixing with liquid crystals behave similar to the elements in the periodic table. These particles give researchers the ability to study the interaction of atoms like hydrogen, helium without having to zoom down to the level of atoms. Scientists demonstrated that for big atoms they could alter their charges with the help of only a switch. It means that particles which were earlier attracted to each other will now repel each other.

Ivan Smalyukh, a physics professor remarked that by having a vast amount of control, scientists can decide on how the particles assemble and which properties they possess. Essentially, it acts like a designer’s toolkit. This toolkit is initiated with a simple material, liquid crystals.

These elements are the ones responsible for brilliant images on our mobile, television screens and are composed of molecules such as rods which all point in one direction. However, in the past decade, researchers observed that if particles like microscopic silica grains are dropped in the liquid crystals, the ordered particles will get altered to make space for the newly added particles.

The remarkable thing is that the bending of the liquid crystals is analogous to the structures possessed by the electron shells in the atoms. The way the liquid crystals bend around the newly added element is very important as when an existent order is disturbed, additional energy is needed to make new arrangements. The problem which scientists faced till now is that they had very less control on the interactions of the big atoms.

Smalyukh’s team used silica in the shape of a hexagon, coated them with a dye which rotates on being exposed to various light types and then added to the liquid crystals. On exposing the mixture to blue light, the molecules would bend in a specific pattern, while it would behave differently on using a different light. The best thing is that no sophisticated laser is needed for these interactions. A normal lamp with a filter is sufficient for it. Which means a bright sunny day is enough for observing the various interactions.

Researchers are quite excited to manipulate these particles by tweaking them in new ways for creating structures not existing in nature and dissolving them similarly.