12 research outputs found
Ultrafast switching of photonic entanglement
To deploy and operate a quantum network which utilizes existing
telecommunications infrastructure, it is necessary to be able to route
entangled photons at high speeds, with minimal loss and signal-band noise,
and---most importantly---without disturbing the photons' quantum state. Here we
present a switch which fulfills these requirements and characterize its
performance at the single photon level; it exhibits a 200-ps switching window,
a 120:1 contrast ratio, 1.5 dB loss, and induces no measurable degradation in
the switched photons' entangled-state fidelity (< 0.002). Furthermore, because
this type of switch couples the temporal and spatial degrees of freedom, it
provides an important new tool with which to encode multiple-qubit states in a
single photon. As a proof-of-principle demonstration of this capability, we
demultiplex a single quantum channel from a dual-channel,
time-division-multiplexed entangled photon stream, effectively performing a
controlled-bit-flip on a two-qubit subspace of a five-qubit, two-photon state
All-optical switching of photonic entanglement
Future quantum optical networks will require the ability to route entangled
photons at high speeds, with minimal loss and added in-band noise, and---most
importantly---without disturbing the photons' quantum state. Here we present an
all-optical switch which fulfills these requirements and characterize its
performance at the single photon level. It exhibits a 200-ps switching window,
120:1 contrast, 1.5-dB loss, and induces no measurable degradation in the
switched photons' entangled-state fidelity (< 0.002). As a proof-of-principle
demonstration of its capability, we use the switch to demultiplex a single
quantum channel from a dual-channel, time-division-multiplexed entangled photon
stream. Furthermore, because this type of switch couples the temporal and
spatial degrees of freedom, it provides an important new tool with which to
encode multiple-qubit quantum states on a single photon
Interaction-Free All-Optical Switching via Quantum-Zeno Effect
We propose a novel interaction-free scheme for all-optical switching which
does not rely on the physical coupling between signal and control waves. The
interaction-free nature of the scheme allows it to overcome the fundamental
photon-loss limit imposed by the signal-pump coupling. The same phenomenon
protects photonic-signal states from decoherence, making devices based on this
scheme suitable for quantum applications. Focusing on waveguides,
we provide device designs for traveling-wave and Fabry-Perot switches. In both
designs, the performance is optimal when the signal switching is induced by
coherent dynamical evolution. In contrast, when the switching is induced by a
rapid dissipation channel, it is less efficient.Comment: 14 pages, 14 figures, submitted to Physical Review
Heralding Single Photons Without Spectral Factorability
Recent efforts to produce single photons via heralding have relied on
creating spectrally factorable two-photon states in order to achieve both high
purity and high production rate. Through a careful multimode analysis, we find,
however, that spectral factorability is not necessary. Utilizing single-mode
detection, a similar or better performance can be achieved with non-factorable
states. This conclusion rides on the fact that even when using a broadband
filter, a single-mode measurement can still be realized, as long as the
coherence time of the triggering photons exceeds the measurement window of the
on/off detector.Comment: 7 pages, 5 figure
Entangled Photon Polarimetry
We construct an entangled photon polarimeter capable of monitoring a
two-qubit quantum state in real time. Using this polarimeter, we record a nine
frames-per-second video of a two-photon state's transition from separability to
entanglement
Maximally entangled mixed states: Creation and concentration
Using correlated photons from parametric downconversion, we extend the
boundaries of experimentally accessible two-qubit Hilbert space. Specifically,
we have created and characterized maximally entangled mixed states (MEMS) that
lie above the Werner boundary in the linear entropy-tangle plane. In addition,
we demonstrate that such states can be efficiently concentrated, simultaneously
increasing both the purity and the degree of entanglement. We investigate a
previously unsuspected sensitivity imbalance in common state measures, i.e.,
the tangle, linear entropy, and fidelity.Comment: 4 pages, 3 figures, 1 table; accepted versio
Erasing Quantum Distinguishability via Single-Mode Filtering
Erasing quantum-mechanical distinguishability is of fundamental interest and
also of practical importance, particularly in subject areas related to quantum
information processing. We demonstrate a method applicable to optical systems
in which single-mode filtering is used with only linear optical instruments to
achieve quantum indistinguishability. Through "heralded" Hong-Ou-Mandel
interference experiments we measure and quantify the improvement of
indistinguishability between single photons generated via spontaneous four-wave
mixing in optical fibers. The experimental results are in excellent agreement
with predictions of a quantum-multimode theory we develop for such systems,
without the need for any fitting parameter.Comment: 5 pages, 5 figure