& Faculty Articles

Dec 28, 2022

^{Credit: Science/AAAS }

Quantum states generally represent the possible conditions of a quantum system in terms of a mathematical entity. For example- the spin of an electron can be either up or down so there are two quantum states and this can further be represented as a superposition using Bra-Ket or Dirac notation.

In principle, quantum states are categorized into two types: pure states and mixed states. A pure state is principally the natural state of a quantum system and carries with it the exact information of the overall system. On the other hand, a mixed state has limited information about a particular quantum system and is usually an ensemble of probabilities. Talking of their representation, pure states are denoted by a ray in a Hilbert space over complex numbers whereas mixed states are represented by density matrices.

Inspired by the infamous Schrodinger’s cat...

Aug 19, 2022

In former works we have addressed the importance of topology in material science and quantum systems.

The word *topology* refers to the contours of a surface or the shape of an object. In mathematics, topology classifies objects by the number of holes they have. A ball is a sphere with no hole, whereas a doughnut, with its one hole, is topologically different. The ball is topologically equivalent to an apple, and a doughnut to a cup, but not to a ball or a pretzel, since going from one topology to another would require a dramatic change, like ripping a hole. This topological feature or state provides a sort of stability to the system, and for this reason, the topological states discovered in some materials are robust and resist disruptions, unless they are as dramatic as the one mentioned previously.

Topological materials provide certain electronic states that persist despite a modification to their physical...

Jul 01, 2022

The Illinois‐Express Quantum Network (IEQNET), a collaboration that includes the DOE's Fermi National Accelerator and Argonne National laboratories, Northwestern University and Caltech, has achieved the first steps toward a functional long-distance quantum network running on telecom fiber optics. Using local fiber optics, the team of researchers successfully deployed the quantum network between two U.S. Department of Energy (DOE) laboratories, 50 kilometers apart.

In this system, information is encoded through quantum entangled photons, and the challenge remains in being able to transfer this information across distances and scales without losing coherence, feature that guarantees that there has been no loss of information. Preserving information is key to any informatic system; all our digital activities require that the information transfer is securely transferred.

A way of measuring the degree of information...

Dec 17, 2021

By Resonance Science Foundation biophysicist William Brown

Quantum spin liquids are exotic phases of matter that offer potential applications in robust quantum information processing with topological qubits. Quantum spin liquids are a phase of matter that feature long-range quantum entanglement involving the magnetic dipoles, or spin, of electrons. Unlike in conventional magnets where the magnetic dipoles of electrons all align and freeze into place, electrons in this new exotic phase are constantly changing and fluctuating like a liquid— leading to one of the most entangled states of matter ever conceived.

Until recent investigations it was unknown if such a highly quantum correlated magnetic state could be realized in an actual physical system. Now, using a 219-atom programmable quantum simulator a team of Harvard researchers have shown that quantum matter and protected quantum information processing are possible with topological spin liquids. Their findings...

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