• Latest CV.
• Latest publication: N.L.Harshman, “Limits on entanglement in rotationally-invariant scattering of spin systems,” Physical Review A 73 (2006), 062326, arXiv: quant-ph/0509013.
• Most recent conference: XXV Workshop on Geometric Methods in Physics, Bialowieza, Poland, 2-8 July 2006.
• Next conference: 3rd Feynman Festival, College Park, Maryland, 25-29 August, 2006.
• I just received a Cottrell College Science Award from the Research Corporation.
  

Brief research summary: I am a theoretical physicist working on questions at the intersection of particle physics and quantum information theory. Currently, the main focus of my research is to understand entanglement in the scattering and decay of elementary quantum systems. By looking at which tensor product structures are invariant under symmetry transformations, I have identified multiple inequivalent types of entanglement for particle systems that are invariant under change of reference frame. Additionally, some of these types of entanglement are also invariant under scattering dynamics. I am extanding this work to different symmetries and using these techniques to investigate specific reaction and decay processes.

• Arno R. Bohm and N.L. Harshman, “On the mass and width of the Z-boson and other relativistic resonances,” Nuclear Physics B 581 (2000) 91-115, arXiv: hep-ph/0001206.
•  A. Bohm, N.L. Harshman, H. Kaldass and S. Wickramasekara, “Time asymmetric quantum theory and the ambiguity of the Z-boson mass and width,” European Physical Journal C 18 (2000), 333-42.
• A. Bohm, N.L. Harshman and H. Walther, “Relating the Lorentzian and exponential: Fermi’s approximation, the Fourier transform and causality,” Physical Review A 66 (2002), 012107, 11 pages, arXiv: quant-ph/0206145.
• N.L. Harshman, “Representations of the Poincaré semigroup and relativistic causality,” International Journal of Theoretical Physics 42 (2003), 2357-2370
• N.L. Harshman, “Visualizing the Mass and Width Spectrum of Unstable Particles,” American Journal of Physics 71 (2003), 984-989, arXiv: physics/0305095.  
• N.L. Harshman and N. Licata*, “Clebsch-Gordan Coefficients for the Extended Quantum-Mechanical Poincarè Group and Angular Correlations of Decay Products,” Annals of Physics 317 (2005), 182-202, arXiv: hep-ph/0407299.
• N.L. Harshman, “Basis States for Relativistic Dynamically-Entangled Particles,” Physical Review A 71 (2005), 022312, 8 pages, arXiv: quant-ph/0409204. Reprinted in Virtual Journal of Quantum Information, March 2005.
• N.L. Harshman,“Dynamical Entanglement and Particle Scaterring,” International Journal of Modern Physics A, 20 (2005) 6220-6228, arXiv: quant-ph/0506212.
• Gary A. Morris, Lee Branum-Martin, Nathan Harshman, Stephen D. Baker, Eric Mazur, Suvendra Dutta, Taha Mzoughi, and Veronica McCauley, “Testing the test: Item response curves and test quality,” American Journal of Physics 74 (2006), 449-453.
• N.L.Harshman, “Limits on entanglement in rotationally-invariant scattering of spin systems,” N.L. Harshman “Limits on entanglement in rotationally-invariant scattering of spin systems,” Physical Review A 73 (2006), 062326, 4 pages arXiv: quant-ph/0509013. Reprinted in Virtual Journal of Quantum Information, July 2006.
• N.L. Harshman, “Poincaré Semigroup Symmetry as an Emergent Property of Unstable Systems,” accepted in International Journal of Theoretical Physics, arXiv: hep-ph/0511298.
• N.L. Harshman, “Dynamical Entanglement in Non-Relativistic, Elastic Scattering,” accepted in International Journal of Quantum Information, arXiv: quant-ph/0606011.
• N.L. Harshman, “Continuous-Discrete Entanglement: An Example with Non-Relativistic Particles,” submitted to Quantum Information and Computation, arXiv: quant-ph/0607138.
• N.L. Harshman and S. Wickramasekara, “Galilean and Dynamical Invariance of Entanglement in Particle Scattering,” submitted to Physical Review Letters, arXinv: quant-ph/0607181.

• A. Bohm and N.L. Harshman, “Quantum Theory in the Rigged Hilbert Space—Irreversibility from Causality,” in Irreversibility and Causality in Quantum Theory—Semigroups and Rigged Hilbert Space, Vol. 504, Springer Lecture Notes in Physics, Eds. A. Bohm, H.-D. Doebner and P. Kielanowski (Springer, Berlin, 1998), pp. 181-237, arXiv: quant-ph/9805063.
• Arno R. Bohm, N.L. Harshman and M. Mithaiwala, “Relativistic Resonances, Relativistic Gamow Vectors and Representations of the Poincaré Semigroup,” in Proceedings of the International Symposium ‘Quantum Theory and Symmetries’, Eds. H.-D. Doebner, V.K. Dobrev, J.-D. Hennig, and W. Leucke, (World Scientific, Singapore, 2000), arXiv:  hep-ph/9912228.
• N.L. Harshman, “Selecting the Mass and Width of Relativistic Resonances,” in Proceedings of the XXIII International Colloquium on Group Theoretical Methods in Physics, Eds. L.G. Mardoyan, G.S. Pogosyan and A.N. Sissakian (JINR Publishing Department, V2,  Dubna, 2002).
• N.L. Harshman, “Kinematic Correlations of Decay Products and the State Spaces of the Relativistic Gamow Vector,” in Proceedings of XXV International Colloquium on Group Theoretical Methods in Physics, IOP Conference Series 185, Eds. G.S. Pogosyan, L.E. Vicent, and K.B. Wolf, (IOP/Canopus, Bristol, 2005), pp. 293-298.

Research summary for students: I am a theoretical physicist who works on topics at the intersection of particle physics and quantum information theory using techniques from group theory. Below, I give details on my research and point to possible applications.

• Particle physics is the study of the smallest and most fundamental chunks of matter and energy. Particles are small enough that the rules of classical mechanics, for example, Newton's Laws, don't work for them in the same way as they work for cars and people and planets. Instead, particle behavior can be best described and predicted using quantum mechanics. Quantum mechanics does not just apply to just to fundamental particles, but also to systems like atoms, molecules, Bose-Einstein condensates, and other systems with extremely small size, low energy, or low temperature.
• Quantum information theory looks at how information is stored and manipulated in systems which follow the rules of quantum mechanics. Information is a very broad term and can mean many thing in different contexts, but in many cases information can be traced down to a physical basis. In computers, that basis is bits, strings of zeros and ones. In biology, information is stored in DNA and RNA sequences. One manifestion of quantum information is called entanglement. Entanglement is a kind of correlation that only occur in quantum systems and to understand it, one must learn about the inherent uncertainty of quantum mechanics and about the superposition principle for probability amplitudes. If you have heard of the Einstein-Rosen-Podolosky paradox or Bell's Inequalities, then you have heard something about entanglement.
• The systems I study usually have many symmetries, and I use these symmetries to help understand quantum systems. What is a symmetry? For example, a sphere (picture a uniform, red ball) has rotational symmetry. No matter how it is rotated, it always looks the same. Some playing cards have top-bottom symmetry: if you flip them they look exactly the same. When a physical system has symmetry, it simplifies how you describe it with mathematics, the natural language of physics. There is a branch of mathematics called group theory that can be used to represent symmetries in quantum mechanics, and it plays a crucial role in my research.
• What are the applications of my research? One hope is that quantum information theory will allow us to build a new generation of computers that will allow hard problems to be solved. "Hard" is actually a technical term here. For example, factoring numbers (which is important for cryptography) is a hard problem; the time it takes to factor a number grows exponentially with the size of the number. There are other applications of entanglement, like quantum encryption and quantum teleportation, which may be useful in communication technology. Even more generally, information is a physical quantity, and there areopen fundamental questions about information and entanglement in particle systems. I don't yet know what the applications could be, but it may open a new window into how we see the world.

Please send me comments, questions, and suggestions about this research description.