Control of conditional quantum beats in cavity QED: amplitude decoherence and phase shifts
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| 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. | |
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00:00
AmplitudeOptical cavityQuantum decoherenceControl systemQuantumElectric power distributionPlain bearingParticle physicsVideoJointMondayInterference (wave propagation)SeeschiffLaserLocherArc lampCrystal structureTheodoliteWeekGround statePaperDayEnergy levelAngeregter ZustandElectronLaserQuantumAmplitudeComputer animationMeeting/Interview
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ElectronMeasurementAM-Herculis-SternGround stateSensorRadioactive decayPhotonEnergy levelAngeregter ZustandLecture/Conference
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PhotonCoherence (signal processing)AM-Herculis-SternAudio frequencyInterference (wave propagation)Absorption (electromagnetic radiation)Radioactive decaySpare partMeasurementElectronic componentAmplitudeGround stateTransmission (mechanics)SensorTransfer functionAngeregter ZustandLecture/Conference
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Order and disorder (physics)Coherence (signal processing)Ground (electricity)MeasurementGround stateDiagram
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Patterson functionOptical cavityAnimal trappingPhotonGaussian beamLightLaserQuantumMagnetizationSpare partPositive feedbackLaserDiffuser (automotive)WolkengattungAtomismTypesettingOrbital periodInterference (wave propagation)YearElektronenkonfigurationShort circuitTransmission (mechanics)Bird vocalizationLecture/Conference
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MagnetismPatterson functionPhotonBestrahlungsstärkeProzessleittechnikInterference (wave propagation)SensorITEREffects unitScrewdriverMeasurementAM-Herculis-SternAtomismOptical cavityDiagram
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Schmitt triggerModulationIntensity (physics)MagnetismSensorPositive feedbackLaserScrewdriverDiagramProgram flowchart
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ElectronWeekInterference (wave propagation)Effects unitPhotonPositive feedbackMagnetic coreLightEnergy levelAmplitudeProzessleittechnikQuantum decoherenceQuantum
Transcript: English(auto-generated)
00:10
Hi, my name is Andre Cimarosti, this is Chris Schroeder, I work with Patterson, and we're here to tell you about the paper we co-authored with Luis Orozco, Howard Carmichael, and
00:21
Pablo Barberis. The title of the paper is Control of Conditional Quantum Beads in Cabinet QED, Amplitude Decoherence, and Phase Shifts. Our experiment exploits quantum interference between indistinguishable paths to demonstrate ground state quantum beads. We have an atom with this electronic energy level structure, two manifold F and F prime,
00:44
each with three Zeeman split sublevels with energy splitting delta E. We start in the Mf equals zero ground state in the F manifold. By applying laser light, we can drive a transition to the Mf equals zero state in the F prime manifold.
01:00
After a characteristic decay time, the atom decays back to the ground state manifold and emits a photon. Conservation of angular momentum allows certain decay pathways, and the ones that we care about are those to the Mf equals plus minus one states. Using polarization measurements on the emitted photon, we can filter out events in which
01:21
the electron decayed to the Mf equals plus or minus one states. However, our polarization measurements cannot tell us which individual level the electron is in, hence it's in a superposition of the Mf equals plus minus one states conditional on the detection of the appropriate photon. Until the absorption of another photon from the drive laser, the phase of each part of
01:43
the superposition evolves at a frequency proportional to the energy splitting, which is of opposite sign for each eigenstate in this superposition. Upon absorption of a photon from the drive, the superposition is coherently excited and is transferred to the F prime manifold.
02:00
Finally, the atom emits a second photon. Using polarization measurements, we filter out the photons which herald decay back to the Mf equals zero state. The probability of this occurring is equal to the square of the associated amplitude, which exhibits beating due to the interference between the opposite sign phase evolutions
02:20
of the components of the ground state superposition. Our data reflects the probability of measuring a second photon conditional on the detection of a first, which heralds the ground state superposition. The data exhibits quantum beats, the amplitude of which gives us a measure of the coherence in the ground state superposition.
02:40
Andreas and Berkeley will now tell you more about our experimental setup and how we implement a feedback mechanism to preserve the coherence in the ground state superposition. This interference, called a quantum beat that Chris just introduced, can be experimentally realized using, for example, rubidium 85 atoms, which we can obtain through an atomic beam.
03:06
Berkeley now will explain a little bit more about the experimental part. In practice, rubidium doesn't come neatly individually packaged in little boxes ready to shine light on, so we need to use an alternative approach.
03:22
What we actually have is a device that produces a diffuse cloud of rubidium, and with an arrangement of lasers and magnetic fields, we can collimate this diffuse cloud into an atomic beam. We could just shine the laser at a small part of this cascade of atoms, but this would make the light interact with many atoms at a time, and the outgoing light
03:42
would be a scattered mess and a nightmare to analyze. So instead, we rely on a clever trick that uses something called an optical cavity. An optical cavity is just basically an arrangement of two mirrors facing each other, and when you shine light in, the light reflects back and forth many times and eventually leaks
04:03
out of it. With this configuration, we can effectively trap a single photon in this cavity for a short period of time. Beyond isolating the interaction between the dry photons and the atom, the cavity also serves to funnel the light that the atoms emit. This makes it much easier to measure in a systematic way.
04:22
The dry photon is vertically polarized, and its interaction with the atom is characterized by the release of a second, circulated polarized photon. As light exits the cavity, we filter out the vertically polarized dry photons with a polarizer and timestamp the arrival of emitted photons at a detector. This process is iterated thousands of times a second for different atoms, and the interference
04:43
can be observed statistically. This beating interference pattern decays over time due to environmental effects, and that is what we aim to control. So what we actually end up doing with our experiment is we use one of our detectors to do some feedback on our experiment, where we turn off momentarily our drive laser.
05:05
This has the effect of increased amplitude on the interference pattern, as you saw before, up to a factor of two, which translates to our superposition living longer and being protected against some decoherence processes.
05:22
Ultimately, what we want to do with our experiment is try to preserve this superposition as long as possible. Many people, especially in the quantum information area, are interested in using atomic superpositions to store information.
05:44
They want to map some information stored in light, for example, into the electronic energy level of an atom, and then extract that and put it back into photons, and then build in this way quantum networks and other devices.
06:03
Our goal for this experiment was simply to keep this superposition alive as long as possible with a fast and very simple feedback system.