Two-state teleportation
Physical Review A - Atomic, Molecular, and Optical Physics 61:6 (2000) 1-8
Abstract:
Quantum teleportation with additional a priori information about the input state achieves higher fidelity than teleportation of a completely unknown state. However, perfect teleporation of two nonorthogonal input states requires the same amount of entanglement as perfect teleportation of an unknown state, namely one ebit. We analyze how well two-state teleportation can be achieved using every degree of pure-state entanglement. We find the highest fidelity of "teleportation" that can be achieved with only classical communication but no shared entanglement. A two-state telecloning scheme is constructed. ©2000 The American Physical Society.Geometric quantum computation
J MOD OPTIC 47:14-15 (2000) 2501-2513
Abstract:
We describe in detail a general strategy for implementing a conditional geometric phase between two spins. Combined with single-spin operations, this simple operation is a universal gate for quantum computation, in that any unitary transformation can be implemented with arbitrary precision using only single-spin operations and conditional phase shifts. Thus quantum geometrical phases can form the basis of any quantum computation. Moreover, as the induced conditional phase depends only on the geometry of the paths executed by the spins it is resilient to certain types of errors and offers the potential of a naturally fault-tolerant way of performing quantum computation.Geometric phases for mixed states in interferometry.
Phys Rev Lett 85:14 (2000) 2845-2849
Abstract:
We provide a physical prescription based on interferometry for introducing the total phase of a mixed state undergoing unitary evolution, which has been an elusive concept in the past. We define the parallel transport condition that provides a connection form for obtaining the geometric phase for mixed states. The expression for the geometric phase for mixed state reduces to well known formulas in the pure state case when a system undergoes noncyclic and unitary quantum evolution.Detection of geometric phases in superconducting nanocircuits.
Nature 407:6802 (2000) 355-358
Abstract:
When a quantum-mechanical system undergoes an adiabatic cyclic evolution, it acquires a geometrical phase factor' in addition to the dynamical one; this effect has been demonstrated in a variety of microscopic systems. Advances in nanotechnology should enable the laws of quantum dynamics to be tested at the macroscopic level, by providing controllable artificial two-level systems (for example, in quantum dots and superconducting devices). Here we propose an experimental method to detect geometric phases in a superconducting device. The setup is a Josephson junction nanocircuit consisting of a superconducting electron box. We discuss how interferometry based on geometrical phases may be realized, and show how the effect may be applied to the design of gates for quantum computation.Information, relative entropy of entanglement, and irreversibility.
Phys Rev Lett 84:10 (2000) 2263-2266