Nuclear magnetic resonance quantum computer

NMR quantum computing uses the spin states of molecules as qubits. NMR differs from other implementations of quantum computers in that it uses an ensemble of systems, in this case molecules. The ensemble is initialized to be the thermal equilibrium state (see quantum statistical mechanics). In mathematical parlance, this state is given by the density matrix:
where H is the hamiltonian matrix of an individual molecule and
where k is the Boltzmann constant and T the temperature.
Operations are performed on the ensemble through RF pulses applied perpendicular to a strong, static field, created by a very large magnet. See Nuclear Magnetic Resonance.
Some early success was obtained in performing quantum algorithms in NMR systems due to the relative maturity of NMR technology. For instance, in 2001 researchers at IBM reported the successful implementation of Shor's algorithm in a 7qubit NMR quantum computer.^{[1]}
However, even from the early days, it was recognized that NMR quantum computers would never be very useful due to the poor scaling of signal to noise in such systems.^{[2]} More recent work, particularly by Caves and others, shows that all experiments in liquid state bulk ensemble NMR quantum computing to date do not possess quantum entanglement, thought to be required for quantum computation. Hence NMR quantum computing experiments are likely to have been only classical simulations of a quantum computer. ^{[3]}
References
 ^ Vandersypen, LMK; Steffen, M; Breyta, G; Yannoni, CS; Sherwood, MH; Chuang, IL. 2001. Experimental realization of Shor's quantum factoring algorithm using nuclear magnetic resonance. NATURE 414 (6866): 883887 <http://dx.doi.org/10.1038/414883a>
 ^ Warren, WS. 1997. The usefulness of NMR quantum computing. SCIENCE 277 (5332): 16881689 <http://www.sciencemag.org/content/277/5332/1688.full>
 ^ Menicucci, NC; Caves, CM. 2002. Local realistic model for the dynamics of bulkensemble NMR information processing. PHYSICAL REVIEW LETTERS 88 (16): art. no.167901 <http://link.aps.org/doi/10.1103/PhysRevLett.88.167901>
Quantum information science General Quantum communication Quantum capacity • Quantum channel • Quantum cryptography (Quantum key distribution) • Quantum teleportation • Superdense coding • LOCC • Entanglement distillationQuantum algorithms Universal quantum simulator • Deutsch–Jozsa algorithm • Grover's search • quantum Fourier transform • Shor's factorization • Simon's Algorithm • Quantum phase estimation algorithm • Quantum annealingQuantum complexity theory Quantum computing models Decoherence prevention Quantum error correction • Stabilizer codes • EntanglementAssisted Quantum Error Correction • Quantum convolutional codesPhysical implementationsQuantum optics Ultracold atoms Spinbased Nuclear magnetic resonance QC • Kane QC • Loss–DiVincenzo QC • Nitrogenvacancy centerSuperconducting quantum computing Charge qubit • Flux qubit • Phase qubitCategories:
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