We propose a new method for proving lower bounds on quantum query algorithms. Instead of a classical adversary that runs the algorithm with one input and then modifies the input, we use a quantum adversary that runs the algorithm with a superposition of inputs. If the algorithm works correctly, its
Universal Lower Bounds for Quantum Diffusion
โ Scribed by J.M. Barbaroux; S. Tcheremchantsev
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 220 KB
- Volume
- 168
- Category
- Article
- ISSN
- 0022-1236
No coin nor oath required. For personal study only.
โฆ Synopsis
We study the connections between dynamical properties of Schro dinger operators H on separable Hilbert space H and the properties of corresponding spectral measures. Our main result establishes a relation for the moment of order p of the form
H dt L , pรd (T ).
(1)
Here L , pรd (T ) is a function connected to the behavior of the Fourier transform of measures in the subclass of measures absolutely continuous with respect to the spectral measure + . Beyond the intrinsic interest of the general formulation (1), this result allows us to derive necessary conditions for dynamical localization in the presence of a pure point spectrum. On the other hand, if we focus on subsequences of time T k Z+ , we can exhibit lower bounds which are, in certain cases, strictly larger than the well-known power-law lower bound for all T expressed in terms of the Hausdorff dimension of spectral measures.
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