Control and enhancement of interferometric coupling between two photonic qubits (original) (raw)

Realization of quantum operations on photonic qubits by linear optics and post-selection

One of the greatest difficulties in the applications of single photon polarization states as qubits is the realization of controlled interactions between two photons. Recently, it has been shown that such interactions can be realized using only beam splitters and high efficiency photon detection by post-selecting a well defined part of the results in the output. We analyze these interactions and discuss schemes for qubit operations based on this mechanism.

Coherently controlled quantum features in a coupled interferometric scheme

Scientific Reports

Over the last several decades, entangled photon pairs generated by spontaneous parametric down conversion processes in both second-order and third-order nonlinear optical materials have been intensively studied for various quantum features such as Bell inequality violation and anticorrelation. In an interferometric scheme, anticorrelation results from photon bunching based on randomness when entangled photon pairs coincidently impinge on a beam splitter. Compared with post-measurement-based probabilistic confirmation, a coherence version has been recently proposed using the wave nature of photons. Here, the origin of quantum features in a coupled interferometric scheme is investigated using pure coherence optics. In addition, a deterministic method of entangled photon-pair generation is proposed for on-demand coherence control of quantum processing.

Quantum-optical state engineering up to the two-photon level

Nature Photonics, 2010

The ability to prepare arbitrary quantum states within a certain Hilbert space is the holy grail of quantum information technology. It is particularly important for light, as this is the only physical system that can communicate quantum information over long distances. We propose and experimentally verify a scheme to produce arbitrary single-mode states of a travelling light field up to the two-photon level. The desired state is remotely prepared in the signal channel of spontaneous parametric down-conversion by means of conditional measurements on the idler channel. The measurement consists of bringing the idler field into interference with two ancilla coherent states, followed by two single-photon detectors, which, in coincidence, herald the preparation event. By varying the amplitudes and phases of the ancillae, we can prepare any arbitrary superposition of zero-, one-and two-photon states.

Quantum Communication without Alignment using Multiple-Qubit Single-Photon States

Physical Review Letters, 2007

We propose a scheme for encoding logical qubits in a subspace protected against collective rotations around the propagation axis using the polarization and transverse spatial degrees of freedom of single photons. This encoding allows for quantum key distribution without the need of a shared reference frame. We present methods to generate entangled states of two logical qubits using present day down-conversion sources and linear optics, and show that the application of these entangled logical states to quantum information schemes allows for alignment-free tests of Bell's inequalities, quantum dense coding and quantum teleportation.

Towards high-fidelity two-photon quantum communications

Fortschritte der Physik, 2003

We propose two alternative scheme for highly efficient nonlinear interaction between weak optical fields. The first scheme is based on the attainment of electromagnetically induced transparency simultaneously for two fields via transitions between magnetically split F = 1 atomic sublevels, in the presence of two driving fields. The second scheme relies on simultaneous electromagnetically-and self-induced transparencies of the two fields. Thereby, equal slow group velocities and giant cross-phase modulation of the weak fields over long distances are achieved.

Photon-mediated qubit interactions in 1D discrete and continous models

In this work we study numerically and analytically the interaction of two qubits in a onedimensional waveguide, as mediated by the photons that propagate through the guide. We develop strategies to assert the Markovianity of the problem, the effective qubit-qubit interactions and their individual and collective spontaneous emission. We prove the existence of collective Lamb-shifts that affect the qubit-qubit interactions and the dependency of coherent and incoherent interactions on the qubit separation. We also develop the scattering theory associated to these models and prove single photon spectroscopy does probes the renormalized resonances of the single-and multi-qubit models, in sharp contrast with earlier toy models where individual and collective Lamb shifts cancel.

Advances in quantum communication using integrated optics

In this paper, we investigate the possibility of increasing the maximal achievable transmission distance of a one-way quantum key distribution link using integrated optical technology on LiNbO 3 . Based on our experience on guided-wave quantum communication, we studied numerically and fabricated a telecom oriented chip that merges all the necessary optical functions at the heart of a quantum relay based on the quantum teleportation scheme. We report here on experimental characterizations in both classical and single photon counting regimes of this first "quantum relay chip" that allow predicting an improvement of the maximal achievable distance by a factor of 1.8.

Optical remote control of a single charge qubit

Physical Review B

Both the electron transport-based qubits, implemented through double quantum dots, and the sources of indistinguishable single photons like self-assembled quantum dots are strong candidates for the implementation of quantum technologies, such as quantum computers and quantum repeaters. Here, we demonstrate a reliable way of coupling these two types of qubits, uncovering the possibility of controlling and reading out the population of the double quantum dot via optical excitation. It is also shown that, in spite of the decoherence mechanisms affecting the qubits, the entanglement between them is achievable and, consequently, the implementation of the suggested system in quantum technologies is feasible.

Control of quantum transverse correlations on a four-photon system

Arxiv preprint arXiv: …, 2011

Control of spatial quantum correlations in bi-photons is one of the fundamental principles of Quantum Imaging. Up to now, experiments have been restricted to controlling the state of a single bi-photon, by using linear optical elements. In this work we demonstrate experimental control of quantum correlations in a four-photon state comprised of two pairs of photons. Our scheme is based on a high-efficiency parametric down-conversion source coupled to a double slit by a variable linear optical setup, in order to obtain spatially encoded qubits. Both entangled and separable pairs have been obtained, by altering experimental parameters. We show how the correlations influence both the interference and diffraction on the double slit.

Synchronized independent narrow-band single photons and efficient generation of photonic entanglement

Physical review letters, 2007

We create independent, synchronized single-photon sources with built-in quantum memory based on two remote cold atomic ensembles. The synchronized single photons are used to demonstrate efficient generation of entanglement. The resulting entangled photon pairs violate a Bell's Inequality by 5 standard deviations. Our synchronized single photons with their long coherence time of 25 ns and the efficient creation of entanglement serve as an ideal building block for scalable linear optical quantum information processing.