Hyperentanglement of photons emitted by a quantum dot

Abstract

Entanglement is a unique quantum mechanical attribute and a fundamental resource of quantum technologies. Entanglement can be achieved in various individual degrees of freedom, nonetheless some systems are able to create simultaneous entanglement in multiple degrees of freedomhyper-entanglement. A hyper-entangled state of light represents a valuable tool capable of reducing the experimental requirements and resource overheads and it can improve the success rate of quantum information protocols. Here, we report on demonstration of polarization and time-bin hyper-entangled photons emitted from a single quantum dot. We achieved this result by applying resonant and coherent excitation on a quantum dot system with marginal fine structure splitting. Our results yield fidelities to the maximally entangled state of 0.81(6) and 0.87(4) in polarization and time-bin, respectively.Quantum dots are semiconductor emitters of quantum light, which makes them material-wise compatible with today's information technologies. Furthermore, the latest advances in the design and implementation of quantum dots shows their competence to efficiently deliver indistingishable single photons [1][2][3] and photon pairs with high degree of entanglement [4,5]. These achievements combined with the possibility of photon storage [6] show the potential of quantum dots to become building blocks of a quantum network [7]. Due to their discrete energy level structure quantum dots are inherently antibunched single photon [8] sources with sub-Poissonian statistics [9] which allows them to produce very pure single photon states [1,2].The application of entanglement of photons includes quantum communications [10,11], where it can be used as resource in information exchange protocols like teleportation [12] and entanglement swapping [13]. In addition, entanglement is an essential element of linear optical quantum computing [14]. The entanglement-enhanced quantum communication schemes such as ultra-dense coding [15] and teleportation [12] enable us, respectively, to transmit two bits in one qubit or securely communicate a quantum state. In such communication schemes the Bell-state-measurements are the crucial element. The simplest realization of a Bell-state measurement uses interference of two photons at a beam-splitter and has the disadvantage that it is efficiency limited [16,17]. The states of light that exhibit entanglement in more than one degree of freedom -hyper-entangled states [18] can be used to perform a complete Bell measurement using linear optics [19,20]. In addition, they are specifically valuable in lowering the resources overhead [21] or for increasing the success rate [22] in the teleportation scheme.Entanglement of photons emitted by quantum dots has been demonstrated in polarization [4,[23][24][25][26][27] and timebin degrees of freedom [28]. The requirements for achieving a high degree of entanglement differ for the two approaches. High degree of polarization entanglement requires the absence of fine structure splitting of the quantum d...

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