Generation And Application Of Frequency Degenerate Twin Beams

Quantum mechanics has always seemed to be the most fascinating branch of physics.In many cases,quantum mechanics is the reason for measurement inaccuracies,and sets the so-called ‘standard quantum limit.' However,quantum mechanics can also provide tools such as entanglement with higher correlation.In this thesis,we describe a series of experiments realized towards the generation of frequency degenerate twin beams using a four-wave mixing(4WM)process in vapor and the cancelation of correlated quantum noise via the SU(1,1)quantum interferometer.We began working on a project using SU(1,1)non-conventional interferometers,which functions as a noise cancelation due to quantum interference with the entanglement and leads to a signal amplification without noise amplification and an improvement in signal-noise-ratio(SNR).We carried out our experiment by selecting nondegenerate four-wave-mixing in atomic vapor as a parametric amplifier to create the quantum-corrected twin beams,We used this parametric amplifier(PA1)to split the input beam into two amplified correlated beams,and then used another parametric amplifier(PA2)as a beam combiner to complete the SU(1,1)interferometer.The improvement in the interferometer's sensitivity was achieved by enhancing the signal level via amplification(PA2)in the interferometer.When adding a stimulated phase modulation in one arm of the experiment,we measured the absolute sensitivity of the phase measurement with a homodyne in an SU(1,1)-type interferometer and obtained a 3dB improvement in sensitivity over a Mach-Zehnder interferometer.Apart from the SU(1,1)project,we turned our attention to the parametric amplifier with atomic vapor.Unlike the previous nondegenerate four-wave-mixing in hot rubidium vapor in a double ? system,We demonstrated a new phase-matching geometry(two-beams-excited emission)in which all four fields propagate in different directions,but two of them are degenerate in frequency.When adopting a parametric amplifier with an injected seed,with the application of two lasers that are locked at 6 GHz frequency difference by a homemade phase-lock-loop(OPLL)system,two types of quantum correlated twin beams(either frequency degenerate or nondegenerate)can be created.I thereby achieved quantum noise reduction,and the intensity difference was nearly 7dB for the nondegenerate type(~6GHz)and nearly 3dB for the degenerate type(~0Hz).Moreover,to seek an application for this new frequency degenerate twin beams,We demonstrate a new type of non-conventional interferometer,which encodes signal information onto one of the EPR correlated beams,and combines the two EPR correlated beams with a 50:50 beam splitter.We obtained two output beams that were in squeezed states,with one squeezed in an X-component and the other in a Y-component.The challenge in realizing this experiment was having higher squeezing and real degenerate frequency.The feedback noise from the OPLL locking system prevented us from achieving a high quality of quantum interference and better squeezing.I constructed a homemade double-pass taper amplifier with an output power of 500 mW for a 200 uW injection,which could amplify the light after the significant frequency shift(6GHz)by AOM.Evading feedback noise,we achieved a nearly 5dB quantum noise reduction and a degenerate frequency below ~0.01 Hz,In order to improve the quantum correlation,I also managed to modulate the atomic energy level with an additional laser counter-propagating to the twin beams to perform as EIT,and we found that the gain in the presence of EIT is strongly enhanced near resonance.