Narrowband Filter for Quantum Light

Narrowband Filter for Quantum Light Alessandro Cerè, Florian Wolfgramm, Mario Napolitano, Morgan W. Mitchell

Morgan W. Mitchell’s group: Quantum Information with Atoms and Light

ICSSUR 09 23 June 2009 - Olomouc

Our Broadband Source The Narrowband Filter Future

Motivation Generation of narrow-band entangled photons for interaction with atomic ensembles Required Spectral Features Resonant with atomic transition of interest Bandwidth comparable with the natural bandwidth of the transition, for 87 Rb Γ ≈6 MHz

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Motivation Generation of narrow-band entangled photons for interaction with atomic ensembles Required Spectral Features Resonant with atomic transition of interest Bandwidth comparable with the natural bandwidth of the transition, for 87 Rb Γ ≈6 MHz

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Our Strategy: Mode Filtering

From the OPO

Filter Single Mode

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From the OPO

Filter Single Mode

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From the OPO

Filter Single Mode

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Outline

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Our Broadband Source OPO setup N00N States Generation

2

The Narrowband Filter Polarization Interferometer Filter Realization Filtering at the Single Photon Level

3

Future Measurements on Atomic Systems

Outline

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OPO setup N00N States Generation

Cavity-Enhanced Down-Conversion

Features Single spatial mode High indistinguishability between the two photons of pair High brightness

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Features of our Source 2 cm long PPKTP crystal Finesse: 80 Pump power: 200 µW Pump wavelength: 397.5 nm Using the available 100 mW of Pump power we can get 4900 pairs/s resonant with the Rb transition A. Cerè

Brightness: 170 000 pairs (s mW)−1

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Features of our Source 2 cm long PPKTP crystal Finesse: 80 Pump power: 200 µW Pump wavelength: 397.5 nm Using the available 100 mW of Pump power we can get 4900 pairs/s resonant with the Rb transition A. Cerè

Brightness: 170 000 pairs (s mW)−1

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Outline

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Indistinguishability

Coincidences counts in 30 s

12

5

x 10

10 8 6 4

Visibility = 0.96

2 0 -4

-2

0

Path difference (mm)

2

4

F. Wolfgramm, X. Xing, A. Cerè, A. Predojevi´c, A. M. Steinberg, and M. W. Mitchell, Opt. Express 16, 18145 (2008) A. Cerè

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Polarization 2-N00N state generation Polarization 2-N00N state √ QWP |1iH |1iV −−−→ (|2iH |0iV + |0iH |2iV ) / 2 Measured Density Matrix* Fidelity=95.2% F. Wolfgramm’s POSTER 31 this afternoon * Following the recipe in R. B. A. Adamson, L. K. Shalm, M. W. Mitchell, and A. M. Steinberg, PRL 98, 043601 (2007) A. Cerè

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Polarization 2-N00N state generation Polarization 2-N00N state √ QWP |1iH |1iV −−−→ (|2iH |0iV + |0iH |2iV ) / 2 Measured Density Matrix* Fidelity=95.2% F. Wolfgramm’s POSTER 31 this afternoon * Following the recipe in R. B. A. Adamson, L. K. Shalm, M. W. Mitchell, and A. M. Steinberg, PRL 98, 043601 (2007) A. Cerè

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Outline

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Polarization Interferometer Filter Realization Single Photon

The Idea It is possible to obtain a filter from the absorptive features of atomic vapors? The problem is similar to Elitzur and Vaidman “Interaction Free” measurements!

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The Idea It is possible to obtain a filter from the absorptive features of atomic vapors? The problem is similar to Elitzur and Vaidman “Interaction Free” measurements!

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Balanced Interferometer

Probe

DH DV

When the Interferometer is balanced, all the light exits through the H output IH

= I0 ,

IV

= 0.

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Unbalanced Interferometer

Probe

DH DV

Inserting a dichroic media, with αR (αL ) indicates the absorption for the right (left) circular polarization. IH IV

α− , 2 α− = I0 e−α+ sinh2 . 2 = I0 e−α+ cosh2

where α+ = (αR + αL )/2 and α− = (αR − αL )/2. A. Cerè

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Electronic Structure and Optical Pumping

Probe

DH Pump

DV

Pump Tuned to the 52 S1/2 (F=2)→52 P1/2 (F’=1) transition (D1 line) Circularly polarized Counter-propagating with the probe

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Outline

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Schematics of the Filter

Enhanced 87 Rb concentration (99:1) Coated-windows cell: losses ≤ 3% External magnetic field reduced to ≤ 1 mG Cell temperature 65◦ C

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A Photo of the Filter

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Filter Transmission in the D1 line

Peak Transmission: 15% Transmission Bandwidth: ≤100 MHz Extinction Ratio: ≥35 dB A. Cerè

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Tunability Tuning the pump beam is possible to address different velocity group into the Doppler profile, effectively tuning the filter transmission peak on a range of ≈1 GHz Normalized Peak Transmission

1 0.8

Optical Pumping Frequency

0.6 0.4 0.2 0 -800

-600

-400

-200

0

200

400

600

800

1000

Pump frequency detuning from the F=2 to the F’=1 transition (MHz)

1200

1400

Filter Transmission Reference Spectroscopy

A. Cerè, V. Parigi, M. Abad, F. Wolfgramm, A Predojevi´c and M. W. Mitchell, Opt. Lett. 34, 1012 (2009) A. Cerè

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Outline

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Filtering of “Single Photons”

Single Photon Probe Average photon number µ ≤ 0.1 per interaction time (average time an atom spend into the probe beam) Collection into Single Mode Fiber Counterpropagating Pump Pumping on a Different Spectroscopic Line: D2 line is 15 nm far away→ efficient dielectric filters (ER≥50dB)

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Filtering of “Single Photons” 1800 1600

Counts/s

1400 1200 1000 800 600 400 200 0

-500

0

500

Probe detuning (MHz)

1000

1500

Statistics of APD clicks while scanning the probe frequency Only one cavity mode of the OPO is efficiently transmitted through the filter! A. Cerè

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Filtering of “Single Photons” 1800 1600

Counts/s

1400 1200 1000 800 600 400 200 0

-500

0

500

Probe detuning (MHz)

1000

1500

Statistics of APD clicks while scanning the probe frequency Only one cavity mode of the OPO is efficiently transmitted through the filter! A. Cerè

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Outline

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Measurements on Atomic Systems

Polarization Rotation in Atomic Ensembles

Goal Maximize information obtained for given number of photons.

Applications Magnetometry Gravity Clocks

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Uncertainty Scaling

Heisenberg Limit

Standard Quantum Limit In classical Polarimetry, the uncertainty is limited by the shot noise √ δφ ∝ 1/ N

For N00N states we talk of “Super-Resolution”, the uncertainty scales linearly with the number of Photons δφ ∝ 1/N

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Uncertainty Scaling

Heisenberg Limit

Standard Quantum Limit In classical Polarimetry, the uncertainty is limited by the shot noise √ δφ ∝ 1/ N

For N00N states we talk of “Super-Resolution”, the uncertainty scales linearly with the number of Photons δφ ∝ 1/N

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Summary

Summary Narrow-band polarization 2-N00N state source Tunable Atomic Filter Resonant with ground state transition Works also at single photon level

Outlook Filter the output of the OPO Use the 2-N00N state for improved sensitivity measurements on atomic ensemble

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The people

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