On Protected Realizations of Quantum Information

There are two complementary approaches to realizing quantum information so that it is protected from a given set of error operators. Both involve encoding information by means of subsystems. One is initialization-based error protection, which involves a quantum operation that is applied before error events occur. The other is operator quantum error correction, which uses a recovery operation applied after the errors. Together, the two approaches make it clear how quantum information can be stored at all stages of a process involving alternating error and quantum operations. In particular, there is always a subsystem that faithfully represents the desired quantum information. We give a definition of faithful realization of quantum information and show that it always involves subsystems. This justifies the "subsystems principle" for realizing quantum information. In the presence of errors, one can make use of noiseless, (initialization) protectable, or error-correcting subsystems. We give an explicit algorithm for finding optimal noiseless subsystems. Finding optimal protectable or error-correcting subsystems is in general difficult. Verifying that a subsystem is error-correcting involves only linear algebra. We discuss the verification problem for protectable subsystems and reduce it to a simpler version of the problem of finding error-detecting codes.Comment: 17 page

Simulations of Information Transport in Spin Chains

Transport of quantum information in linear spin chains has been the subject of much theoretical work. Experimental studies by nuclear spin systems in solid-state by NMR (a natural implementation of such models) is complicated since the dipolar Hamiltonian is not solely comprised of nearest-neighbor XY-Heisenberg couplings. We present here a similarity transformation between the XY-Heisenberg Hamiltonian and the grade raising Hamiltonian, an interaction which is achievable with the collective control provided by radio-frequency pulses in NMR. Not only does this second Hamiltonian allows us to simulate the information transport in a spin chain, but it also provides a means to observe its signature experimentally

An Archaeological Survey of 90 Acres at Camp Bowie, Brown County, Texas

In February, March, and May of 2001, personnel from the Center for Archaeological Research (CAR), The University of Texas at San Antonio, conducted a cultural resource inventory survey, involving pedestrian survey and shovel testing, of an approximately 90-acre (364,060 m2) tract of land in a plowed field on Camp Bowie, Brown County, Texas. A total of 104 shovel tests were systematically placed within the 90-acre area. The survey identified three prehistoric sites, all lithic scatters defined by surface material. Twelve additional shovel tests were placed on these three sites. An arrow point fragment, collected from the surface of 41BR499, suggests a Late Prehistoric affiliation for this site. Dart points collected from 41BR500 suggest a Late Archaic use of this area. Finally, an arrow point, collected from 41BR501, suggests a Late Prehistoric component at this site. In addition, a single whole mano was collected from the surface of 41BR500. Based on the results of the pedestrian survey and the overall condition of the sites, CAR suggests that two of the sites (41BR499 and 41BR501) lack data of sufficient quality or quantity to address regional research questions. In the case of both 41BR499 and 41BR501, the sites appear to be primarily surface phenomena that have been impacted by plowing and are not recommended for inclusion in the National Register of Historic Places, or for designation as State Archeological Landmarks. In the case of 41BR500, while much of the site appears to be disturbed by plowing and trenching activities, a portion of the site situated along the edge of the field has not been disturbed. Subsurface deposits are present in this unplowed area and shovel test results, supported by high soil susceptibility values, suggest the presence of a buried feature. In addition, 41BR500 contains both high artifact density and variety, and the recovery of diagnostic projectile points suggest a Late Archaic temporal placement. As such, CAR recommends that 41BR500 is potentially eligible for inclusion to the National Register of Historic Places, and designation as a State Archeological Landmark. Further testing of this site in the undisturbed portion is recommended to determine final eligibility status

Quantum Simulations on a Quantum Computer

We present a general scheme for performing a simulation of the dynamics of one quantum system using another. This scheme is used to experimentally simulate the dynamics of truncated quantum harmonic and anharmonic oscillators using nuclear magnetic resonance. We believe this to be the first explicit physical realization of such a simulation.Comment: 4 pages, 2 figures (\documentstyle[prl,aps,epsfig,amscd]{revtex}); to appear in Phys. Rev. Let

Subsystem Pseudo-pure States

A critical step in experimental quantum information processing (QIP) is to implement control of quantum systems protected against decoherence via informational encodings, such as quantum error correcting codes, noiseless subsystems and decoherence free subspaces. These encodings lead to the promise of fault tolerant QIP, but they come at the expense of resource overheads. Part of the challenge in studying control over multiple logical qubits, is that QIP test-beds have not had sufficient resources to analyze encodings beyond the simplest ones. The most relevant resources are the number of available qubits and the cost to initialize and control them. Here we demonstrate an encoding of logical information that permits the control over multiple logical qubits without full initialization, an issue that is particularly challenging in liquid state NMR. The method of subsystem pseudo-pure state will allow the study of decoherence control schemes on up to 6 logical qubits using liquid state NMR implementations.Comment: 9 pages, 1 Figur