187 research outputs found
Truly unentangled photon pairs without spectral filtering
We demonstrate that an integrated silicon microring resonator is capable of
efficiently producing photon pairs that are completely unentangled; such pairs
are a key component of heralded single photon sources. A dual-channel
interferometric coupling scheme can be used to independently tune the quality
factors associated with the pump and signal and idler modes, yielding a
biphoton wavefunction with Schmidt number arbitrarily close to unity. This will
permit the generation of heralded single photon states with unit purity.Comment: 5 pages, 3 figure
Optimal Fusion Transformations for Linear Optical Cluster State Generation
We analyze the generation of linear optical cluster states (LOCS) via
addition of one and two qubits. Existing approaches employ the stochastic
linear optical two-qubit CZ gate with success rate of 1/9 per fusion operation.
The question of optimality of the CZ gate with respect to LOCS generation
remains open. We report that there are alternative schemes to the CZ gate that
are exponentially more efficient and show that sequential LOCS growth is
globally optimal. We find that the optimal cluster growth operation is a state
transformation on a subspace of the full Hilbert space. We show that the
maximal success rate of fusing n photonic qubits or m Bell pairs is 1/2^n-1 and
1/4^m-1 respectively and give an explicit optical design
Quantifying Entanglement in a 68-billion Dimensional Quantum State Space
Entanglement is the powerful and enigmatic resource central to quantum information processing, which promises capabilities in computing, simulation, secure communication, and metrology beyond what is possible for classical devices. Exactly quantifying the entanglement of an unknown system requires completely determining its quantum state, a task which demands an intractable number of measurements even for modestly-sized systems. Here we demonstrate a method for rigorously quantifying high-dimensional entanglement from extremely limited data. We improve an entropic, quantitative entanglement witness to operate directly on compressed experimental data acquired via an adaptive, multilevel sampling procedure. Only 6,456 measurements are needed to certify an entanglement-of-formation of 7.11 ± .04 ebits shared by two spatially-entangled photons. With a Hilbert space exceeding 68 billion dimensions, we need 20-million-times fewer measurements than the uncompressed approach and 1018-times fewer measurements than tomography. Our technique offers a universal method for quantifying entanglement in any large quantum system shared by two parties
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