8 research outputs found
Photonic qubits, qutrits and ququads accurately prepared and delivered on demand
Reliable encoding of information in quantum systems is crucial to all
approaches to quantum information processing or communication. This applies in
particular to photons used in linear optics quantum computing (LOQC), which is
scalable provided a deterministic single-photon emission and preparation is
available. Here, we show that narrowband photons deterministically emitted from
an atom-cavity system fulfill these requirements. Within their 500 ns coherence
time, we demonstrate a subdivision into d time bins of various amplitudes and
phases, which we use for encoding arbitrary qu-d-its. The latter is done
deterministically with a fidelity >95% for qubits, verified using a newly
developed time-resolved quantum-homodyne method.Comment: 5 pages, 4 figure
Classical and quantum properties of cylindrically polarized states of light
We investigate theoretical properties of beams of light with non-uniform
polarization patterns. Specifically, we determine all possible configurations
of cylindrically polarized modes (CPMs) of the electro-magnetic field,
calculate their total angular momentum and highlight the subtleties of their
structure. Furthermore, a hybrid spatio-polarization description for such modes
is introduced and developed. In particular, two independent Poincar\'e spheres
have been introduced to represent simultaneously the polarization and spatial
degree of freedom of CPMs. Possible mode-to-mode transformations accomplishable
with the help of conventional polarization and spatial phase retarders are
shown within this representation. Moreover, the importance of these CPMs in the
quantum optics domain due to their classical features is highlighted.Comment: 22 pages, 8 figure
Photonic Quantum Logic with Narrowband Light from Single Atoms
Increasing control of single photons enables new applications of photonic
quantum-enhanced technology and further experimental exploration of fundamental
quantum phenomena. Here, we demonstrate quantum logic using narrow linewidth
photons that are produced under nearly perfect quantum control from a single
^87Rb atom strongly coupled to a high-finesse cavity. We use a controlled- NOT
gate integrated into a photonic chip to entangle these photons, and we observe
non-classical correlations between events separated by periods exceeding the
travel time across the chip by three orders of magnitude. This enables quantum
technology that will use the properties of both narrowband single photon
sources and integrated quantum photonics, such as networked quantum computing,
narrow linewidth quantum enhanced sensing and atomic memories.Comment: 5 pates, 3 figure
How to administer an antidote to Schrodinger's cat
In his 1935 Gedankenexperiment, Erwin Schrödinger imagined a box with a cat and a poisonous substance which has a 50% probability of being released, based on the decay of a radioactive atom. As such, the life of the cat and the state of the poison become entangled, and the fate of the cat is determined upon opening the box. We present an experimental technique that keeps the cat alive on any account. This method relies on the time-resolved Hong-Ou-Mandel effect: two long, identical photons impinging on a beam splitter always bunch in either of the outputs. Interpreting the first photon detection as the state of the poison, the second photon is identified as the state of the cat. Even after the collapse of the first photon's state, we show their fates are intertwined through quantum interference. We demonstrate this by a sudden phase change between the inputs, administered conditionally on the outcome of the first detection, which steers the second photon to a pre-defined output and ensures that the cat is always observed alive
Multimode interferometry for entangling atoms in quantum networks
© 2019 IOP Publishing Ltd. We bring together a cavity-enhanced light-matter interface with a multimode interferometer (MMI) integrated onto a photonic chip and demonstrate the potential of such hybrid systems to tailor distributed entanglement in a quantum network. The MMI is operated with pairs of narrowband photons produced a priori deterministically from a single 87Rb atom strongly coupled to a high-finesse optical cavity. Non-classical coincidences between photon detection events show no loss of coherence when interfering pairs of these photons through the MMI in comparison to the two-photon visibility directly measured using Hong-Ou-Mandel interference on a beam splitter. This demonstrates the ability of integrated multimode circuits to mediate the entanglement of remote stationary nodes in a quantum network interlinked by photonic qubits
Linear optics quantum computing with single photons from an atom-cavity system
One of today’s challenges to realise computing based on quantum mechanics is to reliably and scalably encode information in quantum systems. Here, we present a photon source to on-demand deliver photonic quantum bits of information based on a strongly coupled atom-cavity system. The source operates intermittently for periods of up to 100 μs, with a single-photon repetition rate of 1 MHz, and an intra-cavity production efficiency of up to 85%. Our ability to arbitrarily control the photons’ wavepackets and phase profiles, together with long coherence times of 500 ns, allows to store time-bin encoded quantum information within a single photon. To do so, the spatio-temporal envelope of a single photon is sub-divided in d time bins which allows for the delivery of arbitrary qu-d-its. This is done with a fidelity of > 95% for qubits, and 94% for qutrits verified using a newly developed time-resolved quantum-homodyne measurement technique. Additionally, we combine two separate fields of quantum physics by using our deterministic single-photon source to seed linear optics quantum computing (LOQC) circuits. As a step towards quantum networking, it is shown that this photon source can be combined with quantum gates, namely a chip-integrated beam splitter, a controlled-NOT (CNOT) gate as well as a CNOT4 gate. We use this CNOT4 gate to entangle photons deterministically emitted from our source and observe non-classical correlations between events separated by periods exceeding the travel time across the chip by three orders of magnitude. Additionally, we use time-bin encoded qubits to systematically study the de- and re-phasing of quantum states as well as the the effects of time-varying internal phases in photonic quantum circuits
Multimode interferometry for entangling atoms in quantum networks
We bring together a cavity-enhanced light-matter interface with a multimode interferometer (MMI) integrated onto a photonic chip and demonstrate the potential of such hybrid systems to tailor distributed entanglement in a quantum network. The MMI is operated with pairs of narrowband photons produced a priori deterministically from a single 87Rb atom strongly coupled to a high-finesse optical cavity. Non-classical coincidences between photon detection events show no loss of coherence when interfering pairs of these photons through the MMI in comparison to the two-photon visibility directly measured using Hong-Ou-Mandel interference on a beam splitter. This demonstrates the ability of integrated multimode circuits to mediate the entanglement of remote stationary nodes in a quantum network interlinked by photonic qubits