# New paper: Room-temperature ultra-sensitive mass spectrometer via dynamic decoupling

My new paper with Prof. Nan Zhao was posted on the arXiv yestoday: arXiv:1311.2266. The paper proposed the scheme to detect the tiny mass changing with optically levitated nanodiamond. With the dynamical decoupling method, the mass of the oscillator can be measured by detecting the coherence of the Nitrogen-vacancy center in the nanodiamond. The most suprise feature of the method is that the detecting efficiency is higher in the high temperature than in the low temperature. We believed that the scheme can be used for detecting the mass of single small molecule in room temperature. The title and abstract of the paper is as follows,

Room-temperature ultra-sensitive mass spectrometer via dynamic decoupling

We propose an ultra-sensitive mass spectrometer based on a coupled quantum-bit-oscillator system. Under dynamical decoupling control of the quantum bit (qubit), the qubit coherence exhibits a comb structure in time domain. The time-comb structure enables high precision measurement of oscillator frequency, which can be used as an ultra-sensitive mass spectrometer. Surprisingly, in ideal case, the sensitivity of the proposed mass spectrometer, which scales with the temperature T as T−1/2, has better performance in higher temperature. While taking into account qubit and oscillator decay, we show that the optimal sensitivity is independent on environmental temperature T. With present technology on solid state spin qubit and high-quality optomechanical system, our proposal is feasible to realize an ultra-sensitive mass spectrometer in room temperature.

# New paper: cooling limits and measurement of optomechanical oscillator

New paper dance now.

arXiv:0906.1379

Title: Phase noise and laser cooling limits of opto-mechanical oscillators
Author: Zhang-qi Yin

Abstract: The noise from laser phase fluctuation sets a major technical obstacle to cool the nano-mechanical oscillators to the quantum region. We propose a cooling configuration based on the opto-mechanical coupling with two cavity modes to significantly reduce this phase noise. After optimization of the cavity parameters, we show through simple arguments that the intrinsic cooling limit of the opto-mechanical oscillator is set by $T_{\text{env}}/Q$, where $T_{\text{env}}$ is the environment temperature and $Q$ is the mechanical quality factor. We also discuss detection of the phonon number when the mechanical oscillator is cooled near the quantum region and specify the required conditions for this detection.

Update in 17th June: Today I found a similar paper published in PRL: Three-Mode Optoacoustic Parametric Amplifier: A Tool for Macroscopic Quantum Experiments, by Chunnong Zhao and et al.. The earlier version of the paper was posted in arXiv:0710.2383v3, which didn’t investigate the phase noise in detail and was already cited in my paper.

# Several interesting papers in the last months

It has been for a long time since my last post on quantum physics. Here I select some interesting papers on cavity and optomechanics.

One most interesting paper I read in the last month is from Prof. Vahala and Prof. Painter’s groups. They demonstrated that micro-mechanical oscillator can be driven and cooled by the optical gradient force, other than traditional scattering radiation pressure. This approach makes it possible that photon momentum to be transferred over a length scale approaching the wavelength of light. They use double-disk structure, which provides back-action several orders larger than the previous one. They also demonstrate the cooling factor of 13 dB under heavily damped conditions (mechanical Q=4).

Another paper is discussing the proposal for a search for the cosmic axions using an optical cavity.  Axions, which were postulated 30 years ago, remain an attractive candidate for the cold dark matter of the universe. The proposal uses some stokes-like processes to detect the axions. The axions are absorbed by an optical cavity field of frequency $\omega_o$. The sidebands $\omega_\pm = \omega_0 \pm \omega_a$ appear on the carrier. The displacement of the sidebands is the axion frequency $\omega=E_a=m$. The proposal is very sensitive.

The last one is discussing the possibility of realizing the strong coupling between a mechanical oscillator and a single atom, from Prof. Kimble’s group. The strong coupling between a cavity mode and a single atom has been accomplished for about 10 years. Once the strong coupling between a mechanical oscillator and a single atom was realized, there are countless application the the technique. Everything you have done in the Cavity-QED systems can be transferred to the optomechanical plus atomic systems. It allows us to coherent manipulation, preparation and measurement  of micromechanical objects.

# New paper!

Generating EPR beams in cavity optomechanical system

Abstract: We propose a scheme to produce continuous variable entanglement between phase-quadrature amplitudes of two light modes in optomechanical system. For proper driving power and detuning, the entanglement is insensitive with bath temperature and Q of mechanical oscillator. Under realistic experimental conditions, we find that the entanglement could be very large even at room temperature.

You can read it in arXiv:0811.0424.

Update: the paper has been published in Phys. Rev. A 79, 024301 (2009).

# Normal life started

I have been in USA for a month. I have to say in the last month, my life is not normal. It is different and excited.

Many of people say that there is a culture shock when you enter the different country. I have felt it, though not very intensive. I have to cook myself and lease a apartment once I entered USA. This is totally different life style. I need some time to suit it. Every day I get up in 9:00 am. After breakfast, I go to lab by AATA bus. Around 6:00 pm, I go back home by bus or feet. Every week, I will come to supermarket buy food and other things. Buying food once a week (or two), this is standard American life.

In the apartment, there is no desk and chair and bed. I have to buy it myself. In fact, I only get dinning desk and sofa up to now. So the life in the home is a little tough. For many days, I sleep on the mattress, open my eyes and think something or nothing. Time is killed like this.

Yesterday, internet was OK in my apartment. I feel my normal life comes back. Now the only thing I need to do is buying laptop.

# In U of Mich Now

I came to USA in Sep 23. Now I am in U of Michigan. There are lot of works I must do. I must lease house, complete paper works, check in in International center and my department, and so on. Ann Arbor is a beautiful smal town. Life here is very simple, especially for researchers. When I have my notebook computer and house, I will return to blog.

# New paper

New paper is available now, arXiv:0704.0482

Implementation of holonomic quantum computation through engineering and manipulating environment

Zhang-qi Yin, Fu-li Li and Peng Peng

We consider an atom-field coupled system, in which two multilevel atoms are respectively trapped in two distant cavities which are connected by an optical fiber and are shined by a broadband squeezed light. We show that a two-qubit geometric CPHASE gate between the two atoms can be implemented through adiabatically manipulating the squeezed reservoir along a closed loop. The scheme has two remarkable features. First, no matter how small but nonzero the squeezing amplitude is, a CPHASE gate with arbitrary phase shift can always be implemented. Second, in contrast to previous quantum computation schemes, the larger the effective coupling strength between the environment and the atoms is, the more reliable the realized CPHASE gate is.

In this work, we investigate the possiblility of realizing quantum computation via steering environment, other than controlling Hamiltonian of the quantum systems themselves or choosing measurement strategy. Let me briefly explain our motivation on doing this work.

When building future quantum computer, we must investigate practical systems which could be divided into three subsystems, which are quantum systems, quantum environments and detectors. Up to now, to our knowledge, there are two different types of schemes, controlling the Hamiltonian of quantum systems themselves (see Cirac and Zoller’s paper in 1995) and choosing measurement strategy (such as one-way quantum computer). So it would be interesting to investigate whether it is possible to realize quantum logic gate, such as a two-qubit CPHASE gate, via manipulating quantum environment. Our work reveals this possibility. Therefore, combining our resualts with previous works, we get following insights: Hamiltonians of the quantum systems, environment where quantum systems place and detectors which measure quantum systems, each of them could be manipulated to realize quantum compution.

I believe this work makes our understanding on realizing quantum computation and quantum control more deeply. In doing this work, we got valueable suggestions from Xiao Yun-feng (USTC). I also thank Star Forum where I got valueable suggestions.