A two-mode entangled state was generated experimentally through mixing two squeezed lights from two optical parametric amplifiers on a 50/50 beam splitter.The entangled beams were measured by means of two pairs of balanced homodyne detection systems respectively.The relative phases between the local beams and the detected beams can be locked by using the optical phase modulation technique.The covariance matrix of the two-mode entangled state was obtained when the relative phase of the local beam and the detected beam in one homodyne detection system is locked and the other is scanned.This method provides a way by which one can extract the covariance matrix of any selected quadrature components of two-mode Gaussian state.
We report an experimental observation of a record-breaking ultrahigh rotation frequency about 6 GHz in an optically levitated nanoparticle system. We optically trap a nanoparticle in the gravity direction with a high numerical aperture (NA) objective lens,which shows significant advantages in compensating the influences of the scattering force and the photophoretic force on the trap,especially at intermediate pressure (about100 Pa). This allows us to trap a nanoparticle from atmospheric to low pressure (10^(-3)Pa) without using feedback cooling. We measure a highest rotation frequency about 4.3 GHz of the trapped nanoparticle without feedback cooling and a 6 GHz rotation with feedback cooling,which is the fastest mechanical rotation ever reported to date.Our work provides useful guides for efficiently observing hyperfast rotation in the optical levitation system and may find various applications such as in ultra-sensitive torque detection,probing vacuum friction,and testing unconventional decoherence theories.
The squeezed state was experimentally produced in the four wave mixing process for the first time thirty years ago[1].Its intrinsic nonclassical property has always attracted the attention of the scientists,and it has also presented an unpredictable application potential in quantum information processing[2-6]and quantum metrology[7-9].For gaining an insight into the quantum state,Bertrand et al.[10]introduced the concept of quantum tomography into quantum mechanics in 1987.And in 1997,Breitenbach et al.[11]presented the noise distribution of the squeezed states of light fields and reconstructed the quantum states by balanced homodyne detection(BHD).If the squeezed state light field has a relatively strong amplitude,BHD is not suitable.Consequently,other approaches have also been studied,such as self-tomography of the twin-beam state[12]and self-
The mode splitting in a system with Doppler-broadened high-density two-level atoms in the presence of magnetic field inside a relatively long optical cavity is studied in the superstrong coupling regime(atoms-cavity coupling strength g√N is near or larger than the cavity free-spectral range?FSR).The effect of a magnetic field applied along the quantization axis is used to break the polarization degeneracy of the cavity and thereby introduce birefringence(or Faraday rotation)into the medium.The cavity modes are further split in the presence of the magnetic field compared with the normal case of the multi-normal-mode splitting of the two-level system near the D2 line of87Rb.The dependence of the mode splitting on the magnetic field and the temperature is studied.The theoretical analysis according to the linear dispersion theory can provide a good explanation.
We study a scheme for Mach-Zehnder(MZ) interferometer as a quantum linear device by injecting two-mode squeezed input states into two ports of interferometer.Two-mode squeezed states can be changed into two types of inputs for MZ interferometer:two squeezed states and Einstein-Podolsky-Rosen(EPR) entangled states.The interference patterns of the MZ interferometer vary periodically as the relative phase of the two arms of the interferometer is scanned,and are measured by the balanced homodyne detection system.Our experiments show that there are different interference patterns and periodicity of the output quantum states for two cases which depend on the relative phase of input optical fields.Since MZ interferometer can be used to realize some quantum operations,this work will have the important applications in quantum information and metrology.
We report the measurement of the intensity difference squeezing via the non-degenerate four-wave mixing process in a rubidium atomic vapor medium. Two pairs of balanced detection systems are employed to measure the probe and the conjugate beams, respectively. It is convenient to get the quantum shot noise limit, the squeezed and the amplified noise power spectra. We also investigate the influence of the input extra quadrature amplitude noise of the probe beam. The influence of the extra noise can be minimized and the squeezing can be optimized under the proper parameter condition. We measure the -3.7-dB intensity difference squeezing when the probe beam has a 3-dB extra quadrature amplitude noise. This result is slightly smaller than -4.1 dB when the ideal coherent light (no extra noise) for the probe beam is used.
