Manipulating Photons Based On Rydberg Atoms

Quantum information as a cross subject of quantum mechanics and information science mainly can be divided into quantum communication,quantum computing and quantum measurement.Compared with classical communication,quantum communication has better security.Compared with classical computing,quantum computing has faster calculation speed.Compared with classical measurement,quantum measurement can achieve higher precision and higer sensitivity.The application of quantum information will bring a new technological revolution,which will completely change the development of human society.Photons as the carrier of information have been widely used in both the classical and quantum information fields.Manipulating photons is the basic technology of information processing,including quantum storage,quantum switch,quantum gate,etc.Rydberg atoms have many unique advantages,making quantum information based on Rydberg atoms becomes one of the most popular research directions.Rydberg atom is the highly excited atom containing at least one electron far away from its nucleus.The atomic orbital radius of Rydberg atom is much larger and the lifetime is much longer than that of the low-excited state atom.The interaction between Rydberg atoms is characterized by long-range strong interaction,which is easier to be controlled by external field.The Rydberg atomic system provides an excellent platform for photon manipulation.In this thesis,we mainly study the interaction between Rydberg atoms and the interaction between Rydberg atoms and photons,after which we realize the manipulation on photons by Rydberg atoms.Our work is a crucial step to realize the quantum communication and quantum computing based on Rydberg atoms in the future.The main content of this thesis includes:1.A quantum switch for the true single photon from a polarization entangled photon source based on the Rydberg blockade effect is constructed.We use a self-stabilized system constructed by two BDs in the two paths of atomic spontaneous four-wave mixing(SFWM)process to generate polarization entangled photon pairs.We check the narrow-bandwidth and high-fidelity of our entangled source.We also demonstrate the principle of the self-stability of our system.We perform the switching on and off operation on the true single photon from an entangled photon pair with a switch contrast of 77±3.1%by controlling the Rydberg blockade effect.Finally,we check the fidelity of the entanglement after the switch operation,and confirm that our optical switch would not destroy the original polarization entanglement.2.Experimental research on anomalous Rabi oscillation of the retrieved signal from the Rydberg storage process.Different from previous experiments,we investigate Rabi oscillations of the collective state of photons and atoms between a low-excited state and a Rydberg-excited state.During the reading process of storage,the number of atoms in the low-excited state is continuously converted to the ground state,thus the readout signal shows chirped characteristic.We observe the chirped Rabi oscillation peaks and the fitting curves are given by our formula.3.Experimentally generate entanglement between two Rydberg atomic ensemble located 1 meter apart.We set two magneto-optical traps(MOT)under the same condition in the two paths of a beam displacer(BD).Signal photons can be stored in each magneto-optical trap with the same probability.Finally,the signal photon is retrieved from the storage and detected to check the entanglement between the two Rydberg atomic ensembles.4.Experimental research on the interaction between Rydberg polaritons from two paths with the distance far larger than the blockade radius.There is no crosstalk between two paths.We store the probe photons as Rydberg polaritons,and change the distance between the two storage paths.The interaction between the Rydberg polaritons can still be observed with the distance between two paths four times larger than the blockade radius.In our experiment,we used a single-photon camera with high-resolution imaging to provide experimental evidence for the long-distance interaction between Rydberg polaritons.We also observe the collective Rabi oscillation of retrieved signal photons under the influence of the interaction.The main features and innovations of thesis are:1.For the first time,we experimentally demonstrate switching operation on the true single photon from an entangled photon pair based on the Rydberg blockade effect.Our switch would not destroy the original entanglement of the input photon,and the switch contrast reaches 77±3.1%.Our work provides a new solution for using the Rydberg atomic system to control quantum information network nodes and quantum gating operations.In addition,our experiment has guiding significance for studying the interaction between Rydberg atoms and the entangled photon.2.The anomalous Rabi oscillation between a low-excited state and a Rydberg-excited state during the Rydberg storage process is observed with chirped characteristics.The fitting curves are given by theoretical formula.Our experimental results can achieve on-demand modulation on the wave packets of true single photon.In addition,our work provides a new way to study the collective state of photon and atom.3.We for the first time generate entanglement between two Rydberg atomic ensembles over a long distance.We have realized the process of input,storage and output of entangled states into Rydberg atomic ensemble which is the basic technique for the implementation of quantum communication protocols based on entangled photon sources.Our work is significant in the construction of quantum communication networks and has great value for studying entanglement exchange and entanglement distribution between quantum nodes based on Rydberg atoms.4.The interaction between Rydberg polaritons from two paths separated four times larger than the blockade radius with no crosstalk in space is directly observed by a single photon camera.We find that the maximum interaction distance between Rydberg polaritons is not only dependent on the principle quantum number n,but also can be increased four times larger than the blockade radius by increasing the nonlinearity of Rydberg atomic system through quantum storage process.Increasing the interaction distance between Rydberg polaritons makes it easier to control the long-range interaction.Our work has an important application in constructing quantum simulators by Rydberg atoms.Our works also have value in researching the time evolution of the interaction in many-body physics.