A semiconductor source of triggered entangled photon pairs

Abstract

Entangled photon pairs are an important resource in quantum optics, and are essential for quantum information applications such as quantum key distribution and controlled quantum logic operations. The radiative decay of biexcitons-that is, states consisting of two bound electron-hole pairs-in a quantum dot has been proposed as a source of triggered polarization-entangled photon pairs. To date, however, experiments have indicated that a splitting of the intermediate exciton energy yields only classically correlated emission. Here we demonstrate triggered photon pair emission from single quantum dots suggestive of polarization entanglement. We achieve this by tuning the splitting to zero, through either application of an in-plane magnetic field or careful control of growth conditions. Entangled photon pairs generated 'on demand' have significant fundamental advantages over other schemes, which can suffer from multiple pair emission, or require post-selection techniques or the use of photon-number discriminating detectors. Furthermore, control over the pair generation time is essential for scaling many quantum information schemes beyond a few gates. Our results suggest that a triggered entangled photon pair source could be implemented by a simple semiconductor light-emitting diode.

The role of phonons for exciton and biexciton generation in an optically driven quantum dot

“…Typical values in InGaAs QDs range from almost zero to a few 100 µeV [32,33]. For schemes that are targeted at the preparation of the biexciton state, in order to subsequently initiate a decay cascade that creates entangled photon pairs [12,15,17] it is a necessary precondition to ideally have a vanishing exchange splitting [15,16,34,35]. Otherwise, a kind of which-path information would be introduced in the decay that prevents a high degree of entanglement [14,36].…”

“…The experimental realization of Rabi rotations between the biexciton state and an exciton state [165], as well as between the biexciton and the ground state [149,150,18,151,166,167], which can be both described in the four-level model, has great potential impact on the field of quantum logic where exciton-biexciton systems have been proposed as two-qubit quantum gates [21,165] or as emitters of entangled photon pairs [11,12,13,14,15,16,17,18]. Rabi rotations between the ground and the biexciton state were also preformed by using two-color excitations [168].…”

“…This compatibility with existing technologies makes QDs attractive candidates for a wide range of applications ranging from optoelectronic devices like QD lasers [1,2,3,4], where the target is an improved performance compared to other laser structures, up to new applications in the fields of quantum cryptography or quantum information processing, where the presence of discrete energy levels is mandatory. Examples of such quantum applications are single-photon sources [5,6,7,8,9,10], sources of entangled photon pairs [11,12,13,14,15,16,17,18], and qubit devices or quantum gates [19,20,21,22,23,24]. The functionality of all these latter applications relies on the preparation of a well-defined quantum state.…”

Deterministic entanglement generation between a pair of atoms on different Rydberg states via chirped adiabatic passage

“…It has been demonstrated in a great variety of quantum systems such as photon pairs [1,2], trapped ions [3], atomic ensembles [4,5] and nitrogen-vacancy centers [6,7]. Owing to the weak interactions, the creation of entanglement between neutral atoms in the ground state has to resort to the additional enhancement approaches, such as using a high-Q cavity to mediate the interaction between transient atoms [8] and controlling interatomic collisions by the optical lattice [9].…”

Towards coherent optical control of a single hole spin: Rabi rotation of a trion conditional on the spin state of the hole

“…The ability to grow electronically coupled quantum dots [16] offers the possibility of building a few q-bit register. Whilst, recent demonstrations of non-classical light sources [17,18], and dot in cavity structures with strong single photon optical nonlinearities [19] are examples of potential quantum devices based on semiconductor quantum dots.…”