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 experimentally study optical homodyne and heterodyne detections with the same setup, which is flexible to manipulate the signal sideband modulation. When the modulation only generates a single signal sideband, the light field measurement by mixing the single sideband at ω0 ±? with a strong local oscillator at the carrier frequency ω0on a beam splitter becomes balanced heterodyne detection. When two signal sidebands at ω0 ±? are generated and the relative phase of the two sidebands is locked, this measurement corresponds to optical balanced homodyne detection. With this setup, we may confirm directly that the signal-to-noise ratio with heterodyne detection is two-fold worse than that with homodyne detection. This work will have important applications in quantum state measurement and quantum information.
The study of ultracold Fermi gases has exploded a variety of experimental and theoretical research since the achievement of degenerate quantum gases in the lab,which expands the research range over atomic physics,condensed matter physics,astrophysics and particle physics.Using the Feshbach resonance,one can tune the attractive two-body interaction from weak to strong and thereby make a smooth crossover from the BCS superfluid of cooper pairs to the Bose Einstein condensate of bound molecules.In this crossover regime,the pairing effect plays a significant role in interpreting the interaction mechanism.Whenever the localized or delocalized pairing occurs at sufficiently low temperature,the single-particle energy will shift with respect to free atoms,due to the two-body or many-body interaction.Measuring the pairing gap can improve the understanding of the thermodynamics and hydrodynamics of the phase transition from the pseudogap to the superfluid,which will make an analogue to the high-temperature superconductivity in condensed matter.In this work,we will give a brief introduction to a novel radio-frequency(RF) spectroscopic measurement for pairing gap in an ultracold Fermi gas,which is currently widely used on the ultracold atomic table in the lab.In different interaction regimes of the BEC-BCS crossover,ultracold atoms are excited with a RF pulse and the characteristic behavior can be extracted from the spectrum.
We create weakly bound Feshbach molecules in ultracold Fermi gas 4~K by sweeping a magnetic field across a broad Feshbach resonance point 202.2 G with a rate of 20 ms/G and perform the dissociation process using radio-frequency （RF） technology. From RF spectroscopy, we obtain the binding energy of the weakly bound molecules in the vicinity of Feshbach resonance. Our measurement also shows that the number of atoms generated from the dissociation process is different at various magnetic fields with the same RF amplitude, which gives us a deeper understanding of weakly bound Feshbach molecules.
We investigate sympathetic cooling fermions 40 K by evaporatively cooling bosonic 87 Rb atoms in a magnetic trap with microwave and radio frequency induced evaporations in detail.The mixture of bosonic and fermionic atoms is prepared in their polarized spin states |F=9/2,m F=9/2 for 40 K and |F=2,m F=2 for 87 Rb,which is trapped in Quadrupole-Ioffe-Configuration trap.Comparing microwave with radio frequency evaporatively cooling bosonic 87 Rb atoms with sympathetically cooling Fermi gas 40 K,we find that the presence of rubidium atoms in the |2,1 Zeeman states,which are generated in the evaporative process,gives rise to a significant loss of 40 K due to inelastic collisions.Thus,the rubidium atoms populated in the |2,1 Zeeman states should be removed in order to effectively perform sympathetically cooling 40 K with the evaporatively cooled 87 Rb atoms.
