Reseaches On Quantum Nonlocality And Contextuality By Weak Microwave Signal Detection

Due to the very difference from the classical physics,certain quantum characters especially the quantum nonlocality and quantum contextuality have always been paid much attention.As they are the foundation of quantum communication and quantum computation,researches on these two characteristics are basically important,not only to understand the quantum mechanics,but also for various applications.In the first chapter of the thesis,we introduce certain basic concepts delivered from the original EPR paradox,including the quantum nonlocality and quantum contextuality.This is the basis of our following experimental tests.Some basic technologies on weak microwave signals detection to achieve these tests are also briefly reviewed.The second chapter is focused on the verification of quantum nonlocality.To this end,we build an experimental platform of entangled photons generated by the usual parametric down conversions.Usually,the existence of the quantum nonlocality is checked by testing the violation of the famous Bell inequality.Originally,with the experimentally-demonstrated entangled photons,we obtained the preliminary experimental evidence of the violation of Bell inequality,and the observed Bell function is S = 2.735 ±0.062.Obviously,there is a considerable distance between the present result from the ideal value(2.82).This implies that the choices of the measurement basis are not optimal.By using the quantum tomographic technology,we optimized the basis of the measurement of the optimization,and then got the new Bell function value as:S = 2.772±0.063.This is a greater violation of the Bell inequality.During this test,some new technologies to enhance up the output power of the used semiconductor laser were developed to meet the needs of our experimental tests.The third chapter is our digital experiments to verify the quantum contextuality.It is well-known that the simplest physical system used for verifying the quantum contextuality is a qutrit(or three levels)system.However,it is necessary to carry out the expected non-destructive measurement of quantum states with sufficient high fidelity.To this end,we proposed an approach by using microwave cavity transmission spectral technique to realize the nondestructive measurements of the three-level atomic quantum state.It is shown that the locations and relatively-heights of the observed transmitted spectra can mark the relevant quantum states and their superposed probabilities.Therefore,by observing the transmission spectra of the driven microwave cavity the quantum states of the three-level system in the cavity can be determined.Secondly,in order to overcome the difficulty for the implementations of joint measurements,we simplify the contextuality inequality with joint measurements into the mathematically-equivalent forms with only the single-body measurements.As the consequence,the Kochen-Specker inequality can be tested simply.We perform the numerical experiments,with the driven cavity quantum electrodynamics system,and verify the violations of the Kochen-Specker inequality.Similarly,such a numerical experiment has been generalized into the test the violation of the another Kocken-Specker-like inequality,i.e.,the so-called KCBS inequality,which is state independent version of the original Kochen-Specker inequality.In the fourth chapter,we briefly summarize our works on the fabrication of superconducting transition-edge-sensing(TES)single photon detector,which is particularly important for various optical experiments for verifying quantum coherences.Note that the semiconductor photon detectors used widely in the current experiments do not,in fact,met the requirements of the high quantum efficiency to close the detection holes.Thus,the TES detector is particularly important,as it can achieve the expected high quantum efficiency,approaching to 100%.As the first step work for implementing the TES single-photon detection,we have to fabricate the chip of the TES detector by using of micro-technology.With the existing device-prepared and tested platforms in our laboratory,we have fabricated the preliminary TES devices and realized their resistance-temperature relation measurements in ultra-low temperature.The observed superconducting transition characteristics are useful for the next steps to achieve high efficiency single photon detections.The preparations and manipulations of the photonic orbital angular momentum are reported in the fifth chapter.As we know that the orbital angular momentum of the photon is another kind of physical freedoms,beside the polarizations.Physically,the orbital angular momentum of the photon possesses more information than the usual spin angular momentum,and thus it will provide more information processing applications in future.Using spatial light modulator,we experimentally realized the synthesis and characterization of photon orbital angular momentum.This implies that the higher-dimensional Bell inequality can be tested by using the photon orbital angular momentum degrees of freedom.In the sixth chapter,we generalize our researches on cavity quantum electrodynamics into the coherent manipulations of photon bunching effects.We show how such a effect can be manipulated by controlling the quantum coherence of the atoms in the driven cavity.Finally,we summarize our works and prospect the possible further researches in the future.