Quantum Storage of Orbital Angular Momentum Entanglement in an Atomic Ensemble

Abstract

Constructing a quantum memory for a photonic entanglement is vital for realizing quantum communication and network [1][2][3][4]. Besides enabling the realization of high channel capacity communication [5], entangled photons of high-dimensional space are of great interest because of many extended applications in quantum information and fundamental physics fields [6][7][8][9]. Photons entangled in a two-dimensional space had been stored in different system [10][11][12][13], but there have been no any report on the storage of a photon pair entangled in a high-dimensional space. Here, we report the first experimental realization of storing an entangled orbital angular momentum (OAM) state through a far off-resonant two-photon transition (FORTPT) in a cold atomic ensemble. We reconstruct the matrix density of an OAM entangled state postselected in a two-dimensional subspace with a fidelity of 90.3%±0.8% and obtain the Clauser, Horne and Shimony and Holt inequality parameter S of 2.41±0.06 after a programmed storage time. All 2 results clearly show the preservation of entanglement during the storage. Besides, we also realize the storage of a true-single-photon via FORTPT for the first time.The establishment of quantum network in the future needs distribution of quantum entangled photons over channels between different nodes [14,15]. To overcome the exponential scaling of the error rate with the channel length, the concept of quantum repeater is introduced [16], which combines entanglement swapping and quantum memory to efficiently extend the achievable distance of quantum communication. During the last years, important progresses have been made towards the realization of an efficient and coherent quantum memory based on gas and solid atomic ensemble [17][18][19][20][21], photons encoded in a two-dimensional space spanned for example by orthogonal polarizations or different paths had been stored [10][11][12][13]. Moreover, many groups and researchers are active in storing light encoded using a high-dimensional space in different physical systems [22][23][24][25][26][27][28][29][30][31][32]. In quantum information and quantum optics fields, a photon encoded in a high-dimensional space [33][34][35][36] could carry 2 log d bits information, where d is the number of orthogonal basis vectors of the Hilbert space. In such a way, the transmission rate of quantum communications is increased greatly [37], and the capacity of channel could be also significantly improved [5]. Moreover, it affords quantum key distribution a more secure flux of information [38], etc. Because of the inherent infinite dimension of orbital angular momentum (OAM) space [39][40][41], a light is usually encoded in OAM space to offer the higher-information-density coding. Therefore, the preparation of a high-dimensional OAM entangled state plays a vital role inquantum information and communication fields, and usually was realized by using the spontaneous parametric down-conversion in a crystal [41] or spontaneous Raman scattering (SRS) in an atomic ens...

Two-photon entanglement in multiqubit bidirectional-waveguide QED

“…Finally, we point out that such a longer sustained entanglement is necessary in performing certain quantum information processing protocols (see Refs. [44][45][46] and applications mentioned therein).…”

Comparison of beam generation techniques using a phase only spatial light modulator

“…They are characterised by two parameters, a winding number and a radial order p, however for this investigation we restrict ourselves to modes with p = 0 and define a LaguerreGaussian mode of order to be LG . Within this set we have chosen three test beams: a simple fundamental Gaussian LG 0 , a single Laguerre-Gaussian mode of moderate order (LG 10 ) and a spatially intricate superposition of LG modes |LG 3 + αLG 11 | 2 ; α = | , known as an optical Ferris wheel [6]. A final test is made with a non-propagating field shape: a scene of an appropriately named 'Laser class' sailboat.…”

“…It was the advent of spatial light modulators (SLMs) which made the breakthrough to arbitrary beam generation, allowing flexible beam shaping in a wide range of applications including optical tweezers [3], quantum information [4], coherence tuning, atom trapping [5][6][7][8] and storage [9,10] amongst others. Light, by nature, is intrinsically complex, and to gain full control of a light field one must be able to arbitrarily specify both the phase and amplitude profile.…”

Multiqubit entanglement in bidirectional-chiral-waveguide QED

“…See Refs. [35][36][37] and the applications mentioned therein. One straightforward way to accomplish this task is to isolate the system from the environment, that is, by setting γ iL = γ iR = 0.…”