250 research outputs found
Quantum data gathering
Measurement of a quantum system – the process by which an observer gathers information about it – provides a link between the quantum and classical worlds. The nature of this process is the central issue for attempts to reconcile quantum and classical descriptions of physical processes. Here, we show that the conventional paradigm of quantum measurement is directly responsible for a well-known disparity between the resources required to extract information from quantum and classical systems. We introduce a simple form of quantum data gathering, “coherent measurement”, that eliminates this disparity and restores a pleasing symmetry between classical and quantum statistical inference. To illustrate the power of quantum data gathering, we demonstrate that coherent measurements are optimal and strictly more powerful than conventional one-at-a-time measurements for the task of discriminating quantum states, including certain entangled many-body states (e.g., matrix product states)
Unification and limitations of error suppression techniques for adiabatic quantum computing
While adiabatic quantum computation (AQC) possesses some intrinsic robustness
to noise, it is expected that a form of error control will be necessary for
large scale computations. Error control ideas developed for circuit-model
quantum computation do not transfer easily to the AQC model and to date there
have been two main proposals to suppress errors during an AQC implementation:
energy gap protection and dynamical decoupling. Here we show that these two
methods are fundamentally related and may be analyzed within the same
formalism. We analyze the effectiveness of such error suppression techniques
and identify critical constraints on the performance of error suppression in
AQC, suggesting that error suppression by itself is insufficient for
fault-tolerant, large-scale AQC and that a form of error correction is needed.
This manuscript has been superseded by the articles, "Error suppression and
error correction in adiabatic quantum computation I: techniques and
challenges," arXiv:1307.5893, and "Error suppression and error correction in
adiabatic quantum computation II: non-equilibrium dynamics," arXiv:1307.5892.Comment: 9 pages. Update replaces "Equivalence" with "Unification." This
manuscript has been superseded by the two-article series: arXiv:1307.5892 and
arXiv:1307.589
- …