For any quantum algorithm operating on pure states we prove that the presence of multi-partite entanglement, with a number of parties that increases unboundedly with input size, is necessary if the quantum algorithm is to offer an exponential speed-up over classical computation. Furthermore we prove that the algorithm can be classically efficiently simulated to within a prescribed tolerance η e...

Quantum entangled states have become one of the key resources in the rapidly expanding field of quantum information processing and computation [1, 2, 3, 4]. Nevertheless, the study of physical character and mathematical structure of the quantum entanglement is far from being satisfied. One even does not have a general criterion to judge if a quantum (mixed) state is entangled or not. For bipart...

Quantum information theory and quantum computing are theoritical basis of quantum computers. Thanks to entanglement, quantum mechanical systems are provisioned to realize many information processing problems faster than classical counterparts. For example, Shor’s factorization algorithm, Grover’s search algorithm, quantum Fourrier transformation, etc. Entanglement, is the theoretical basis prov...

Heralded entanglement between macroscopical samples is an important resource for present quantum technology protocols, allowing quantum communication over large distances. In such protocols, optical photons are typically used as information and entanglement carriers between macroscopic quantum memories placed in remote locations. Here we investigate theoretically a new implementation which empl...

Quantum entangled states are playing fundmental roles in quantum information processing such as quantum computation, quantum teleportation, dense coding, quantum cryptographic schemes quantum error correction, entanglement swapping, and remote state preparation (RSP) etc.. However the theory of quantum entanglement is still far from being satisfied. To quantify the degree of entanglement a numb...

Superposition is a critical property of quantum system resulting in quantum coherence and quantum entanglement. Quantum coherence and also entanglement provide the important resource for quantum information processing, for example, Deutschs algorithm, Shors algorithm, teleportation, superdense coding and quantum cryptography [1]. As with any such resource, there arises naturally the question of...

Entanglement, viz. the non-separability of quantum states, is a fundamental prediction of quantum mechanics, which is at odds with the classical perception of reality. Furthermore, it constitutes a resource for quantum computation and quantum communication. Electronic degrees of freedom in nanostructures – in particular the spin – constitute promising candidates to implement quantum information...

Entanglement--one of the most delicate phenomena in nature--is an essential resource for quantum information applications. Scalable photonic quantum devices must generate and control qubit entanglement on-chip, where quantum information is naturally encoded in photon path. Here we report a silicon photonic chip that uses resonant-enhanced photon-pair sources, spectral demultiplexers and reconfi...

We consider one-way quantum state merging and entanglement distillation under compound and arbitrarily varying source models. Regarding quantum compound sources, where the source is i.i.d., but the source state an unknown member of a certain set of density matrices, we continue investigations begun in Ref. 7 and determine the classical as well as entanglement cost of state merging. We further i...

Entanglement between a single photon and a quantum memory forms the building blocks for a quantum repeater and quantum network. Previous entanglement sources are typically with low retrieval efficiency, which limits future larger-scale applications. Here, we report a source of highly retrievable spin-wave-photon entanglement. Polarization entanglement is created through interaction of a single ...