# Ancilla-assisted enhancement of channel estimation for low-noise parameters

## Abstract

In order to make a unified treatment for estimation problems of a very small noise or a very weak signal in a quantum process, we introduce the notion of a low-noise quantum channel with one noise parameter. It is known in several examples that prior entanglement together with nonlocal output measurement improves the performance of the channel estimation. In this paper, we study this 'ancilla-assisted enhancement' for estimation of the noise parameter in a general low-noise channel. For channels on two level systems we prove that the enhancement factor, the ratio of the Fisher information of the ancilla-assisted estimation to that of the original one, is always upper bounded by 3/2. Some conditions for the attainability are also given with illustrative example000.

- Authors:

- Department of Physics, Faculty of Science, Tohoku University, Aoba-ku, Sendai, 980-8578 (Japan)
- Graduate School of Information Sciences, Tohoku University, Aoba-ku, Sendai, 980-8579 (Japan)

- Publication Date:

- OSTI Identifier:
- 20786486

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Physical Review. A; Journal Volume: 72; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevA.72.052334; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 74 ATOMIC AND MOLECULAR PHYSICS; NOISE; PERFORMANCE; QUANTUM COMPUTERS; QUANTUM ENTANGLEMENT; QUANTUM INFORMATION; QUANTUM MECHANICS; SIGNALS

### Citation Formats

```
Hotta, Masahiro, Karasawa, Tokishiro, and Ozawa, Masanao.
```*Ancilla-assisted enhancement of channel estimation for low-noise parameters*. United States: N. p., 2005.
Web. doi:10.1103/PHYSREVA.72.0.

```
Hotta, Masahiro, Karasawa, Tokishiro, & Ozawa, Masanao.
```*Ancilla-assisted enhancement of channel estimation for low-noise parameters*. United States. doi:10.1103/PHYSREVA.72.0.

```
Hotta, Masahiro, Karasawa, Tokishiro, and Ozawa, Masanao. Tue .
"Ancilla-assisted enhancement of channel estimation for low-noise parameters". United States.
doi:10.1103/PHYSREVA.72.0.
```

```
@article{osti_20786486,
```

title = {Ancilla-assisted enhancement of channel estimation for low-noise parameters},

author = {Hotta, Masahiro and Karasawa, Tokishiro and Ozawa, Masanao},

abstractNote = {In order to make a unified treatment for estimation problems of a very small noise or a very weak signal in a quantum process, we introduce the notion of a low-noise quantum channel with one noise parameter. It is known in several examples that prior entanglement together with nonlocal output measurement improves the performance of the channel estimation. In this paper, we study this 'ancilla-assisted enhancement' for estimation of the noise parameter in a general low-noise channel. For channels on two level systems we prove that the enhancement factor, the ratio of the Fisher information of the ancilla-assisted estimation to that of the original one, is always upper bounded by 3/2. Some conditions for the attainability are also given with illustrative example000.},

doi = {10.1103/PHYSREVA.72.0},

journal = {Physical Review. A},

number = 5,

volume = 72,

place = {United States},

year = {Tue Nov 15 00:00:00 EST 2005},

month = {Tue Nov 15 00:00:00 EST 2005}

}