Timothy C. Ralph | |
---|---|

Born | |

Citizenship | Australia |

Known for | Quantum computing, Quantum cryptography |

Scientific career | |

Fields | quantum optics, quantum information science |

Institutions | University of Queensland, Australian National University, University of Auckland |

**Tim C. Ralph** is an Australian physicist who specializes in the application of quantum optics to quantum information science and quantum computing. He is Professor in Physics at the University of Queensland, and Program Manager in the ARC Centre for Quantum Computer and Communication Technology.^{ [1] } Ralph is known for developing continuous variable quantum cryptography ^{ [2] } and co-founder of measurement based computation with continuous variable optics.^{ [3] } In 2012, Ralph was one of the scientists responsible for establishing quantum discord as a computational resource.^{ [4] } As of 2012, Tim has 200 publications and over 4500 citations. He has co-authored "A guide to experiments in quantum optics". His publications include 23 in Physical Review Letters, 6 in the Nature suite of journals, as well as articles in Science and Reviews of Modern Physics.

- 2006 ARC Professorial Fellowship
- 2000 ARC QEII Fellowship

- A guide to experiments in quantum optics. Vol. 1. Weinheim: wiley-vch, 2004.

- Tim C. Ralph: Biography. Center for quantum computation and communication technology.

**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.

In quantum computing, a **quantum algorithm** is an algorithm which runs on a realistic model of quantum computation, the most commonly used model being the quantum circuit model of computation. A classical algorithm is a finite sequence of instructions, or a step-by-step procedure for solving a problem, where each step or instruction can be performed on a classical computer. Similarly, a quantum algorithm is a step-by-step procedure, where each of the steps can be performed on a quantum computer. Although all classical algorithms can also be performed on a quantum computer, the term quantum algorithm is usually used for those algorithms which seem inherently quantum, or use some essential feature of quantum computation such as quantum superposition or quantum entanglement.

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.

**Pieter Kok** is a Dutch physicist and one of the co-developers of quantum interferometric optical lithography.

**Artur Konrad Ekert** FRS is a British-Polish professor of quantum physics at the Mathematical Institute, University of Oxford, professorial fellow in quantum physics and cryptography at Merton College, Oxford, Lee Kong Chian Centennial Professor at the National University of Singapore and the founding director of the Centre for Quantum Technologies (CQT). His research interests extend over most aspects of information processing in quantum-mechanical systems, with a focus on quantum communication and quantum computation. He is best known as one of the pioneers of quantum cryptography.

In physics, **interaction-free measurement** is a type of measurement in quantum mechanics that detects the position, presence, or state of an object without an interaction occurring between it and the measuring device. Examples include the Renninger negative-result experiment, the Elitzur–Vaidman bomb-testing problem, and certain double-cavity optical systems, such as Hardy's paradox.

Within quantum technology, a **quantum sensor** utilizes properties of quantum mechanics, such as quantum entanglement, quantum interference, and quantum state squeezing, which have optimized precision and beat current limits in sensor technology. The field of quantum sensing deals with the design and engineering of quantum sources and quantum measurements that are able to beat the performance of any classical strategy in a number of technological applications. This can be done with photonic systems or solid state systems.

**Daniel Amihud Lidar** is the holder of the Viterbi Professorship of Engineering at the University of Southern California, where he is a Professor of Electrical Engineering, Chemistry, Physics & Astronomy. He is the Director and co-founder of the USC Center for Quantum Information Science & Technology (CQIST) as well as Scientific Director of the USC-Lockheed Martin Quantum Computing Center, notable for his research on control of quantum systems and quantum information processing.

**Quantum cryptography** is the science of exploiting quantum mechanical properties to perform cryptographic tasks. The best known example of quantum cryptography is quantum key distribution which offers an information-theoretically secure solution to the key exchange problem. The advantage of quantum cryptography lies in the fact that it allows the completion of various cryptographic tasks that are proven or conjectured to be impossible using only classical communication. For example, it is impossible to copy data encoded in a quantum state. If one attempts to read the encoded data, the quantum state will be changed due to wave function collapse. This could be used to detect eavesdropping in quantum key distribution (QKD).

**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..

In quantum information theory, **quantum discord** is a measure of nonclassical correlations between two subsystems of a quantum system. It includes correlations that are due to quantum physical effects but do not necessarily involve quantum entanglement.

**Linear optical quantum computing** or **linear optics quantum computation** (**LOQC**) is a paradigm of quantum computation, allowing universal quantum computation. LOQC uses photons as information carriers, mainly uses linear optical elements, or optical instruments to process quantum information, and uses photon detectors and quantum memories to detect and store quantum information.

**Integrated quantum photonics,** uses photonic integrated circuits to control photonic quantum states for applications in quantum technologies. As such, integrated quantum photonics provides a promising approach to the miniaturisation and scaling up of optical quantum circuits. The major application of integrated quantum photonics is Quantum technology:, for example quantum computing, quantum communication, quantum simulation, quantum walks and quantum metrology.

The **six-state protocol (SSP)** is the quantum cryptography protocol that is the version of BB84 that uses a six-state polarization scheme on three orthogonal bases.

**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.

**Crispin William Gardiner** is a New Zealand physicist, who has worked in the fields of Quantum Optics, Ultracold Atoms and Stochastic Processes. He has written about 120 journal articles and several books in the fields of quantum optics, stochastic processes and ultracold atoms

**Giacomo Mauro D'Ariano** is an Italian quantum physicist. He is a professor of theoretical physics at the University of Pavia, where he is the leader of the QUIT group. He is a member of the Center of Photonic Communication and Computing at Northwestern University; a member of the Istituto Lombardo Accademia di Scienze e Lettere; and a member of the Foundational Questions Institute (FQXi).

**Warwick Bowen** is an Australian quantum physicist and nanotechnologist at The University of Queensland. He leads the Quantum Optics Laboratory, is Director of the UQ Precision Sensing Initiative and is one of three Theme Leaders of the Australian Centre for Engineered Quantum Systems.

**Relativistic quantum cryptography** is a sub-field of quantum cryptography, in which in addition to exploiting the principles of quantum physics, the no-superluminal signalling principle of relativity theory stating that information cannot travel faster than light is exploited too. Technically speaking, relativistic quantum cryptography is a sub-field of relativistic cryptography, in which cryptographic protocols exploit the no-superluminal signalling principle, independently of whether quantum properties are used or not. However, in practice, the term relativistic quantum cryptography is used for relativistic cryptography too.

The **Eastin–Knill theorem** is a no-go theorem that states: "No quantum error correcting code can have a continuous symmetry which acts transversely on physical qubits". In other words, no quantum error correcting code can transversely implement a universal gate set. Since quantum computers are inherently noisy, quantum error correcting codes are used to correct errors that affect information due to decoherence. Decoding error corrected data in order to perform gates on the qubits makes it prone to errors. Fault tolerant quantum computation avoids this by performing gates on encoded data. Transversal gates, which perform a gate between two "logical" qubits each of which is encoded in *N* "physical qubits" by pairing up the physical qubits of each encoded qubit, and performing independent gates on each pair, can be used to perform fault tolerant but not universal quantum computation because they guarantee that errors don't spread uncontrollably through the computation. This is because transversal gates ensure that each qubit in a code block is acted on by at most a single physical gate and each code block is corrected independently when an error occurs. Due to the Eastin–Knill theorem, a universal set like {*H, S*, CNOT, *T*} gates can't be implemented transversally. For example, the *T* gate can't be implemented transversely in the Steane code. This calls for ways of circumventing Eastin–Knill in order to perform fault tolerant quantum computation. In addition to investigating fault tolerant quantum computation, the Eastin–Knill theorem is also useful for studying quantum gravity via the AdS/CFT correspondence and in condensed matter physics via quantum reference frame or many-body theory.

- ↑ "Centre for Quantum Computer and Communication Technology". Archived from the original on 15 February 2011.
- ↑ Ralph, T. C. (8 December 1999). "Phys. Rev.A 61 (2000) 010302".
*Physical Review A*.**61**(1): 010303. arXiv: quant-ph/9907073 . doi:10.1103/PhysRevA.61.010303. - ↑ Menicucci, N. C.; Van Loock, P.; Gu, M.; Weedbrook, C.; Ralph, T. C.; Nielsen, M. A. (2006). "Physical Rev Lett 97.11 (2006): 110501" (PDF).
*Physical Review Letters*.**97**(11): 110501. arXiv: quant-ph/0605198 . doi:10.1103/PhysRevLett.97.110501. PMID 17025869. S2CID 14715751. - ↑ "University of Queensland News".

This page is based on this Wikipedia article

Text is available under the CC BY-SA 4.0 license; additional terms may apply.

Images, videos and audio are available under their respective licenses.

Text is available under the CC BY-SA 4.0 license; additional terms may apply.

Images, videos and audio are available under their respective licenses.