# Quantum Physics

Mysterious phenomena appear in the quantum world beyond our ordinary imagination, from elementary particles through atoms, molecules and matter. This quantum world also has intimate relation to the beginning of Universe.

Now, not only understanding this amazing world, but also we are advancing in manipulation and control of quantum phenomena, and developing various applications in our daily life.

## Academic Staff

### Takayuki MIYADERA

Associate Professor (Graduate School of Engineering)

**Research Theme**

Foundations of Quantum Physics, Quantum Information Theory.

**Classes**

Quantum Physics I, Quantum Physics II, Fundamentals of Nuclear Physics, Quantum Field Theory, Advanced Quantum Physics.

**Contact Information**

E-mail: miyadera@deletethis.nucleng.kyoto-u.ac.jp

### Kenzo OGURE

Assistant Professor (Graduate School of Engineering)

**Research Theme**

- Early universe and Particle Physics: Early universe and Particle Physics (Baryogenesis, Dark matter), Finite Temperature Field Theory, Neutrino physics
- Solitons in Field Theory : Topological Soliton, non-Topological Soliton
- Spin Glass and Information Theory: Spin Glass, Replica Method, Application of Statistical Method to Information Theory

**Contact Information**

Katsura Campus, C3 Bldg. d1S02

TEL: +81-75-383-3909

E-mail: ogure@* (Add "nucleng.kyoto-u.ac.jp" after @)

## Research Topics

### Quantum state manipulation and its application for quantum communication

A quantum state can be transferred to a distant place by using an entangled state, Einstein-Podolsky-Rosen pair, which is called quantum teleportation. Extensive studies have been done for its realization mainly with the polarization and also the quadrature components of optical field.

We study the teleportation-based manipulation of photon number states, where higher dimensional states as well as qubit are available for more efficient information processing and communication scheme. In practice, we have recently proposed a unique method to generate a maximally entangled state via swapping from a pair of squeezed vacuum states by performing the number-sum and phase-difference measurement.

We also consider the quantum Zeno effect. That is, the time evolution of quantum system may be suppressed or even controlled by making frequent measurements. It will be applicable for quantum state manipulation.

### Leptogenesis and baryogenesis via multiscalar coherent evolution

Universe consists dominantly of matter and radiation, and very little anti-matter. The generation of baryon number asymmetry (baryogenesis) hence should occur in the early universe after the inflation epoch. Baryogenesis is an important subject in particle physics and cosmology.

We study baryogenesis in supersymmetric electroweak models. Specifically, we have found by investigating the supersymmetric Higgs triplet model that some scalar fields together start coherent evolution after the inflation with large initial field values. Through this multiscalar evolution involved with lepton number and CP violations, the lepton number asymmetry can be generated efficiently, i.e., leptogenesis. It is then converted in significant fraction to the baryon number asymmetry via electroweak anomalous effect.

In some supersymmetric models including the Higgs triplet model and the neutrino see-saw model with right-handed neutrinos, we investigate further this mechanism of leptogenesis and its implications in phenomenology such as neutrino masses and mixings, and lepton flavor violating processes.

### Rydberg atom cavity detector of microwave photons and dark matter axion search

Universe is thought to be filled in significant fraction with "dark matter", which is not luminous; perhaps about 30% with dark matter, and the rest mostly with dark energy. Neutrinos and axion are good candidates of dark matter. Since such particles have very weak interactions with ordinary matter, special methods should be developed to detect them.

We apply cavity quantum electrodynamics (cavity QED) for promising detection method of dark matter axion. Axions can be converted resonantly to microwave photons in a cavity under a strong magnetic field of about 10Tesla. Then, these photons are detected with Rydberg atoms which are excited by absorbing them, and the background due to thermal radiation can be suppressed sufficiently by cooling down the cavity to low temperature about 10mK. We perform theoretical evaluation of this quantum method for photon counting, providing the ultra-sensitive dark matter axion search.

Absorption of photon by Rydberg atom

Axion, an unknown particle