Entangled quantum states in high-dimensional space show many advantages compared with entangled states in two-dimensional space.The former enable quantum communication with higher channel capacity,enable more efficient quantum-information processing and are more feasible for closing the detection loophole in Bell test experiments.Establishing high-dimensional entangled memories is essential for long-distance communication,but its experimental realization is lacking.We experimentally established high-dimensional entanglement in orbital angular momentum space between two atomic ensembles separated by 1 m.We reconstructed the density matrix for a three-dimensional entanglement and obtained an entanglement fidelity of(83.9±2.9)%.More importantly,we confirmed the successful preparation of a state entangled in more than three-dimensional space(up to seven-dimensional)using entanglement witnesses.Achieving high-dimensional entanglement represents a significant step toward a high-capacity quantum network.
Indispensable for quantum communication and quantum computation,quantum memory executes on demand storage and retrieval of quantum states such as those of a single photon,an entangled pair or squeezed states.Among the various forms of quantum memory,Raman quantum memory has advantages forits broadband and high-speed characteristics,which results in a huge potential for applications in quantum networks and quantum computation.However,realising Raman quantum memory with true single photons and photonic entanglementis challenging.In this review,after briefly introducing the main benchmarks in the development of quantum memory and describing the state of the art,we focus on our recent experimental progress inquantum memorystorage of quantum states using the Raman scheme.
Light-carrying orbital angular momentum(OAM)has great potential in enhancing the information channel capacity in both classical and quantum optical communications.Long distance optical communication requires the wavelengths of light are situated in the low-loss communication windows,but most quantum memories currently being developed for use in a quantum repeater work at different wavelengths,so a quantum interface to bridge the wavelength gap is necessary.So far,such an interface for OAM-carried light has not been realized yet.Here,we report the first experimental realization of a quantum interface for a heralded single photon carrying OAM using a nonlinear crystal in an optical cavity.The spatial structures of input and output photons exhibit strong similarity.More importantly,single-photon coherence is preserved during up-conversion as demonstrated.
Are quantum states real? This most fundamental question in quantum mechanics has not yet been satisfactorily resolved, although its realistic interpretation seems to have been rejected by various delayedchoice experiments. Here, to address this long-standing issue, we present a quantum twisted double-slit experiment. By exploiting the subluminal feature of twisted photons, the real nature of a photon during its time in flight is revealed for the first time. We found that photons' arrival times were inconsistent with the states obtained in measurements but agreed with the states during propagation. Our results demonstrate that wavefunctions describe the realistic existence and evolution of quantum entities rather than a pure mathematical abstraction providing a probability list of measurement outcomes. This finding clarifies the long-held misunderstanding of the role of wavefunctions and their collapse in the evolution of quantum entities.
We report low pump power high-efficiency frequency doubling of a fundamental laser beam at 795 nm, corresponding to the rubidium D1 line, to generate UV light at 397.5 nm using a periodically poled KTi OPO4（PPKTP） crystal in a ring cavity. We obtain maximum stable output power of 49 m W for mode-matching pump power of 110 m W, corresponding to 45% raw efficiency（56% net efficiency when considering the output coupling mirror’s 80% transmission）. This is the highest efficiency obtained at this wavelength in PPKTP with such low pump power. We obtain 80% beam coupling efficiency to single-mode fiber, demonstrating high beam quality.
In this Letter, we report on the successful optical storage of orbital angular momentum（OAM） using Rydberg electromagnetically induced transparency（EIT） in cold rubidium atoms. With a storage time of 1.4 μs, the retrieved structure is highly similar, showing the ability of storing light＇s OAM at a principal quantum number of 20. The results at higher principal quantum numbers（n ？ 25; 30） are also measured. These results show the promise of image processing based on a Rydberg atomic system.
The long-range interaction between Rydberg-excited atoms endows a medium with large optical nonlinearity.Here,we demonstrate an optical switch to operate on a single photon from an entangled photon pair under a Rydberg electromagnetically induced transparency configuration.With the presence of the Rydberg blockade effect,we switch on a gate field to make the atomic medium nontransparent thereby absorbing the single photon emitted from another atomic ensemble via the spontaneous fourwave mixing process.In contrast to the case without a gate field,more than 50%of the photons sent to the switch are blocked,and finally achieve an effective single-photon switch.There are on average 1-2 gate photons per effective blockade sphere in one gate pulse.This switching effect on a single entangled photon depends on the principal quantum number and the photon number of the gate field.Our experimental progress is significant in the quantum information process especially in controlling the interaction between Rydberg atoms and entangled photon pairs.
Yi-Chen YuMing-Xin DongYing-Hao YeGuang-Can GuoDong-Sheng DingBao-Sen Shi
