Atmospheric continuous-variable quantum communication
This is a modal window.
The media could not be loaded, either because the server or network failed or because the format is not supported.
Formal Metadata
| Title |
| |
| Title of Series | ||
| Number of Parts | 49 | |
| Author | ||
| License | CC Attribution 3.0 Unported: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
| Identifiers | 10.5446/38704 (DOI) | |
| Publisher | ||
| Release Date | ||
| Language |
Content Metadata
| Subject Area | ||
| Genre | ||
| Abstract |
|
00:00
Electric power distributionQuantumParticle physicsPlain bearingVideoComputer animation
00:03
Kette <Zugmittel>PhotographyAM-Herculis-SternCommunications satelliteKontraktionMorse codeData conversionMeeting/Interview
00:34
Light
00:47
WavelengthLaserContinuous waveAM-Herculis-Stern
00:59
FiberStagecoachMercury switchRotationGaussian beamOptical tableAM-Herculis-SternAngeregter ZustandSpare partSpread spectrumCash register
01:06
Electronic componentModulationBusReceiver (radio)Coherent statesAngeregter ZustandPlatingDiffractionMultiplexNegativer WiderstandAudio frequencyStagecoachZeitdiskretes SignalSignal (electrical engineering)ApertureGaussian beamQuantum fluctuationFormation flyingGround stationStationeryGenerationAM-Herculis-SternMusical ensembleIntensity (physics)Transverse modeSchwache LokalisationMinuteScreen printingKleinsignalverhaltenDistortionJitter-EffektAtmosphärische Turbulenz
02:35
Intensity (physics)Transmission (mechanics)Field-effect transistorElectric power distributionTransmission (mechanics)Kette <Zugmittel>Gaussian beamSpaceflightDiagram
02:45
Electronic componentTelephoneSensorAngeregter ZustandNegativer WiderstandStellar atmosphereSignal (electrical engineering)Contrast (vision)Quantum fluctuationPhase (matter)Antenna (radio)Quantization (physics)Musical ensembleYearSchwache LokalisationMeasurementPhotonStray lightSingle (music)MultiplexAM-Herculis-SternHomodynempfängerEffects unit
03:17
Angeregter ZustandAmplitudePhased arrayMeasurementRoll formingFlugbahnMembrane potentialAntenna (radio)Effects unitKette <Zugmittel>Electric power distributionStellar atmosphereQuantumComputer animation
Transcript: English(auto-generated)
00:08
Hi there, this is Christian Pointinger and I am Bettina Heim and we would like to tell you about our quantum communication experiment over a free-space point-to-point link of 1.6 km in the city of Erlangen in Germany.
00:21
We study atmospheric influences on the capability of the link to act as a continuous variable quantum channel. We use polarization encoding which is in particularly robust against atmospheric influences. This aerial photo gives an impression of a free-space link in the city of Erlangen. In a truly urban environment, it connects the building of the Max Planck Institute for the Science of
00:41
Light with a tall building of the Department of Computer Science of the Friedrich Alexander University, Erlangen, Nuremberg. The setup of the sender is placed in a technical supply room on the roof of our institute's building. A continuous-wave laser beam at a wavelength of 809 nm is guided by a polarization maintaining single-mode fiber to an out-coupling stage on a breadboard.
01:03
This breadboard is mounted on a rotation tilt stage for beam alignment and can easily be exchanged. A bright circularly polarized beam is sent through two electro -optical modulators which introduce small signal components in the orthogonal polarization. A half-wave plate in between of these modulators allows to realize a
01:24
two-dimensional signal state generation, so in principle any modulation format can be used. We focus on the discrete modulation of coherent states that are strongly overlapping and thus nearly indistinguishable. The generated states now contain the signal encoding as well as a low-cost oscillator, polarization multiplexed and in the same spatial mode.
01:45
This beam is then further guided by two mirrors and expanded by a telescope to a diameter of approximately 4 cm. After that, it leaves the sender setup and is sent towards the receiver. This is an outer view of the sender.
02:03
On its way to the receiver that is currently shown, the corner beam passes buildings, trees and streets. This heterogeneous environment contributes to atmospheric turbulence by which the beam gets distorted and diverges more than expected by the diffraction limit.
02:20
We recorded the arriving beam seen on the screen. As you can see, the beam suffers from both wavefront distortions and beam wandering or spatial jitter. The beam is clipped as the receiver aperture is smaller than the chittering arriving beam. Thus, the received intensity fluctuates. We were able to increase the overall link transmission to 76%.
02:43
A telescope is used to demagnify and collimate the arriving beam. The signal states are measured in a double homodyne detection, which in our scheme is realized as a simultaneous measurement of the S1 and S2 Stokes parameters. This directly reveals the Q-function of the states. For polarization multiplex setting, phase fluctuations are intrinsically auto-compensated
03:04
as both signal and local oscillator undergo the same atmospheric fluctuations. In contrast to single photon detection techniques, the influence of stray light on the scheme is negligible. We finally interpret the measured data by using the framework of effective
03:20
entanglement and determine optimal working points with respect to the distributed effective entanglement. The high entanglement transmission rates that our system can achieve indicate the strong potential of atmospheric links in the field of continuous variable quantum field distribution.