Barbara Kraus (born 26 December 1975) [1] ) is an Austrian physicist specializing in quantum information, quantum entanglement, and quantum key distribution. She is a University Professor at the TUM School of Natural Sciences at the Technical University of Munich.
Kraus is originally from Innsbruck. [2] She studied mathematics and physics at the University of Innsbruck, earning diplomas in mathematics and physics. She completed her PhD in physics under the supervision of Ignacio Cirac in 2003. After postdoctoral research at the Max Planck Institute of Quantum Optics, the University of Geneva, and the University of Innsbruck, she became an assistant professor in Innsbruck in 2010, and earned her habilitation there in 2012. [3] She became full professor in 2020. [4] In 2023 she was appointed professor of Quantum Algorithms and Applications at the Technical University of Munich. [5]
Kraus is best known for her work in quantum information and especially in entanglement theory. Together with her coworkers she developed criteria to decide whether a quantum state is separable or entangled and showed how to construct optimal entanglement witnesses [6] and studied the creation of entanglement by unitary quantum gates [7] and dissipative processes. [8] In 2010 she showed how to decide whether two pure quantum states of a many-particle system are equivalent to each other in terms of entanglement. [9] More recently she introduced the notion of "maximally entangled sets" as a new concept generalizing maximally entangled states to the case of considering entanglement between more than two systems (multipartite entanglement). [10] In the field of quantum cryptography, she studied the security of key-distribution protocols and the achievable secret-key rates. Among other results, she and her collaborators Renato Renner and Nicolas Gisin gave an influential information-theoretic security proof for the security of a quantum key distribution protocol [11]
Kraus won a Start-Preis from the Austrian Science Fund in 2010. [3] She was the 2011 winner of the Ludwig Boltzmann Prize of the Austrian Physical Society, [12] [13] and the 2013 winner of the Lieben Prize of the Austrian Academy of Sciences for her work on many-body entanglement. [2] She became a member of the Young Academy of the Austrian Academy of Sciences in 2014. [14]
Quantum entanglement is the phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical and quantum physics: entanglement is a primary feature of quantum mechanics not present in classical mechanics.
A Bell test, also known as Bell inequality test or Bell experiment, is a real-world physics experiment designed to test the theory of quantum mechanics in relation to Albert Einstein's concept of local realism. Named for John Stewart Bell, the experiments test whether or not the real world satisfies local realism, which requires the presence of some additional local variables to explain the behavior of particles like photons and electrons. To date, all Bell tests have found that the hypothesis of local hidden variables is inconsistent with the way that physical systems behave.
In quantum mechanics, separable states are quantum states belonging to a composite space that can be factored into individual states belonging to separate subspaces. A state is said to be entangled if it is not separable. In general, determining if a state is separable is not straightforward and the problem is classed as NP-hard.
In physics, in the area of quantum information theory, a Greenberger–Horne–Zeilinger state is a certain type of entangled quantum state that involves at least three subsystems. The four-particle version was first studied by Daniel Greenberger, Michael Horne and Anton Zeilinger in 1989, and the three-particle version was introduced by N. David Mermin in 1990. Extremely non-classical properties of the state have been observed. GHZ states for large numbers of qubits are theorized to give enhanced performance for metrology compared to other qubit superposition states.
The W state is an entangled quantum state of three qubits which in the bra-ket notation has the following shape
Time-bin encoding is a technique used in quantum information science to encode a qubit of information on a photon. Quantum information science makes use of qubits as a basic resource similar to bits in classical computing. Qubits are any two-level quantum mechanical system; there are many different physical implementations of qubits, one of which is time-bin encoding.
Quantum cloning is a process that takes an arbitrary, unknown quantum state and makes an exact copy without altering the original state in any way. Quantum cloning is forbidden by the laws of quantum mechanics as shown by the no cloning theorem, which states that there is no operation for cloning any arbitrary state perfectly. In Dirac notation, the process of quantum cloning is described by:
In quantum information and quantum computing, a cluster state is a type of highly entangled state of multiple qubits. Cluster states are generated in lattices of qubits with Ising type interactions. A cluster C is a connected subset of a d-dimensional lattice, and a cluster state is a pure state of the qubits located on C. They are different from other types of entangled states such as GHZ states or W states in that it is more difficult to eliminate quantum entanglement in the case of cluster states. Another way of thinking of cluster states is as a particular instance of graph states, where the underlying graph is a connected subset of a d-dimensional lattice. Cluster states are especially useful in the context of the one-way quantum computer. For a comprehensible introduction to the topic see.
Quantum lithography is a type of photolithography, which exploits non-classical properties of the photons, such as quantum entanglement, in order to achieve superior performance over ordinary classical lithography. Quantum lithography is closely related to the fields of quantum imaging, quantum metrology, and quantum sensing. The effect exploits the quantum mechanical state of light called the NOON state. Quantum lithography was invented at Jonathan P. Dowling's group at JPL, and has been studied by a number of groups.
In the case of systems composed of subsystems, the classification of quantum-entangledstates is richer than in the bipartite case. Indeed, in multipartite entanglement apart from fully separable states and fully entangled states, there also exists the notion of partially separable states.
Jens Eisert is a German physicist, ERC fellow, and professor at the Free University of Berlin. He is also affiliated with the Helmholtz Association and the Fraunhofer Society.
Frank Verstraete is a Belgian quantum physicist who is working on the interface between quantum information theory and quantum many-body physics. He pioneered the use of tensor networks and entanglement theory in quantum many body systems. He holds the Leigh Trapnell Professorship of Quantum Physics at the Faculty of Mathematics, University of Cambridge, and is professor at the Faculty of Physics at Ghent University.
Andrew G. White FAA is an Australian scientist and is currently Professor of Physics and a Vice-Chancellor's Senior Research Fellow at the University of Queensland. He is also Director of the University of Queensland Quantum technology Laboratory; Deputy-Director of the ARC Centre for Engineered Quantum systems, and a Program Manager in the ARC Centre for Quantum Computer and Communication Technology..
Hans Jürgen Briegel is a German theoretical physicist. He is Full Professor at the University of Innsbruck and conducts research in the field of quantum physics and quantum information.
Quantum complex networks are complex networks whose nodes are quantum computing devices. Quantum mechanics has been used to create secure quantum communications channels that are protected from hacking. Quantum communications offer the potential for secure enterprise-scale solutions.
Sandu Popescu is a Romanian-British physicist working in the foundations of quantum mechanics and quantum information.
Continuous-variable (CV) quantum information is the area of quantum information science that makes use of physical observables, like the strength of an electromagnetic field, whose numerical values belong to continuous intervals. One primary application is quantum computing. In a sense, continuous-variable quantum computation is "analog", while quantum computation using qubits is "digital." In more technical terms, the former makes use of Hilbert spaces that are infinite-dimensional, while the Hilbert spaces for systems comprising collections of qubits are finite-dimensional. One motivation for studying continuous-variable quantum computation is to understand what resources are necessary to make quantum computers more powerful than classical ones.
Spin squeezing is a quantum process that decreases the variance of one of the angular momentum components in an ensemble of particles with a spin. The quantum states obtained are called spin squeezed states. Such states have been proposed for quantum metrology, to allow a better precision for estimating a rotation angle than classical interferometers. Recently, it was shown that these states cannot provide a better precision.
Bound entanglement is a weak form of quantum entanglement, from which no singlets can be distilled with local operations and classical communication (LOCC).
In quantum physics, the "monogamy" of quantum entanglement refers to the fundamental property that it cannot be freely shared between arbitrarily many parties.