Alpha Immersion Hands- on Ac4vi4es. Kiko Galvez Colgate University 2015

Transcription

1 lpha Immersion Hands- on c4vi4es Kiko Galvez Colgate University

2 c4vity I (Tuesday M) - Basic lignment Goal: To get hands- on experience with op4cal alignments. Materials: 2 x5 op4cal breadboard HeNe laser 3 mirrors with mounts (, B, C) Iris and mount, 4 ¼- 20 screws/knurled knobs 2

3 c4vity I (Tues. M): Basic lignment 6 12 HeNe laser 11.5 B C 1. dd mirror. lign reflec4on with iris and knurled screws. 2. dd mirror B (with straight edge). Reflec4on must be close to the edge of the mirror. lign reflec4on with iris and knurled screws according to instruc4ons in the next page. 3. dd mirror C. lign reflec4on with iris and knurled screws. 3

4 c4vity I (Tues. M) cont. ligning the beam to be parallel to the holes in the breadboard/op4cal table. 4

5 c4vity II (Tuesday M) Parametric down- conversion Goal: To set- up and measure photon counts produced by spontaneous parametric down- conversion. Materials: Hardware: Flip- mirror (F) Plumb- bob and extra iris with mount Plate with 1- m radius curvature GaN (blue) diode laser BBO crystal and mount (X1) Folding mirror on transla4on stage (D) 2 fiber collimators (with iris is if available) on mounts 2 mul4mode fibers (D and DB) 2 band- pass filters Beam dump (K) Electronics: 2 single- photon detectors, ltera board, PC with labview (will use program Mdyn2015i or Mdynrduino15 )

6 c4vity II (Tues. M) cont. Parametric Down Conversion (2) HeNe laser (5) plate B (3) (4) 1. Remove mirror C. 2. Make a pencil mark X where the crystal will go (in path of the HeNe beam and 14 from leb edge of the breadboard). 3. Place three + marks 1- m away from X as shown (3 degree from each other- 1 m away, 3 degrees is 5.2 cm in the transverse direc4on). Use plumb bob. 4. Place plate with 1- m radius of curvature (if available) over marks. 6

7 c4vity II (Tues. M) cont. Collimator alignment (2) HeNe laser iris Cheap mirror 5(b) 5(a) B 5(c) Place collimator with fiber in path of HeNe beam and against the plate, and align it so that light comes out of the other end of the fiber. Use mirrors and iris. This is a cri4cal step: a. Place collimator (without fiber) so it is centered on the beam. Expanded beam must be centered; if not then collimator is not centered. b. Hold cheap mirror against collimator and adjust collimator mount s 4lt so that beam is reflected straight back. Once done, check that expanded beam is centered, otherwise repeat (a). c. Put fiber and look for light coming out of the other end. djust the 4lt of the collimator so that beam is as narrow as possible and as bright as possible. d. Connect collimator to detector fiber DB. 7

8 c4vity II (Tues. M) cont. ligning the second collimator HeNe laser F (6) iris B (2) DB (7) 6. Insert Flipper mirror (F) and align its posi4on and 4lt so that the beam to goes over the 3 rd + mark. Use plumb bob and iris. 7. Place second collimator in the path of the beam and against the plate so that the light comes at the other end of the fiber (repeat previous step #5 for this alignment). 8. Connect collimator to detector fiber D. 8

9 c4vity II (Tues. M) cont. Pukng it all together (9) D F B Blue laser (8) (10) iris HeNe laser (13) X1 8. Flip the mirror. 9. Place blue laser and mirror on stage (D) to send the beam through the middle path shown. Use plumb bob and iris. 10. Place the down conversion crystal over the x. 11. Place filters in front of the collimators. 12. Turn off the lights. Turn on the electronics. Look for coincidences B. 13. Maximize coincidences by (1 st ) 4l4ng the crystal, (2 nd ) 4l4ng the collimators, and (3 rd ) transla4ng (slightly!) one of the collimators along the track. They should be more than accidental coincidences: N acc = N N B T where T = 50ns (rule of thumb if N =N B =10k - > N acc = 5). (11) (13) DB D Beam dump (K) 9

10 c4vity III (Tuesday M/PM) Single- photon existence and the Hanbury- Brown- Twist Test Goals: To prove that photons exist. Measurement of the an4- correla4on parameter. Materials (mounts are pedestal type): Hardware: Prism polarizer (N) Glan Thompson Polarizer (T) 3 rd Fiber collimator and fiber (DC) 3 rd Bandpass filter 10

11 c4vity III (Tues. PM): Sekng up the HBT test. HeNe laser DC F N T D B DB DC Blue laser 1. Place polarizing beam splirer (aligned 45 rela4ve to the horizontal) in the path of the red aligning laser. 2. Place the Thompson prism T aber the polarizer. 3. lign the third collimator and fiber to transmit the red light deflected by the prism. 4. Connect the collimator to detector fiber DC 11

12 c4vity III (Tues. PM) cont. Measuring the an4- correla4on parameter g HeNe laser DC F N T D B DB DC Blue laser 5. Take measurements for 1 minute. 6. Hanbury- Brown- Twiss test: compute 7. The error is approximately Δg = g N BC g = N BC N N B N C if g < 1 then you are measuring single photons! 12

13 c4vity IV (Tuesday PM) Single- photon interference Goals: To set- up a zero- path- difference Mach- Zehnder interferometer. Measure single- photon interference. Materials (mounts are pedestal type): Hardware: 2 iden4cal broadband NIR beam splirers with mounts (G). 1 mirror with mount (I). 1 mirror (iden4cal to previous) on a transla4on stage (H). Piezo electric stack added as spacer to stage. Diverging lens and mount (L) Electronics: DC card/module (we use GPIB- driven SRS245 interface module) or rduino- based D/. x10-15 voltage amplifier (for piezo) PC spectrometer (we use Ocean Op4cs) Small incandescent light bulb 13

14 c4vity IV (Tues. PM): Sekng up an interferometer. HeNe laser F D B Blue laser The interferometer will be set up in the outlined region. See next steps in sekng up the interferometer. 14

15 c4vity III (Tues. PM): Sekng up an interferometer (BE SCRUPULOUS!). H (2) H (1) G G G I (3) H (4) H (5) H L G G G (6) G I I G G I 1. Insert beam splirer G. lign 90 reflec4on with irises and knurled knobs. 2. Insert mirror on linear stage H. lign 90 reflec4on with irises and knurled knobs. 3. Insert mirror on mount I. lign reflec4on with irises and knurled knobs. 4. Insert 2 nd beam splirer G. lign reflec4on with irises and knurled knobs. 5. djust transla4on stage so that the two beams overlap. They should not be ver4cally displaced. If they are, there is a bad reflec4on that has to be redone. 6. dd diverging lens L to expand the beam and adjust 4lt of second beam splirer for broadest fringes 15

16 c4vity IV (Tues. PM): Sekng up an interferometer- cont. (10) (7) Incandescent bulb (8) (9) Spectrometer/PC 7. Place the fiber mount and spectrometer looking into the output of the interferometer. 8. Place an incandescent bulb at the input of the interferometer. 9. Observe the fringes of the spectrum. 10. Broaden the fringes by transla4ng the stage. 11. Remove the bulb and spectrometer and allow HeNe beam to go through the interferometer. Check that the interferometer is s4ll aligned. 12. If previous is nega4ve, align and repeat (7)- (10). 16

17 c4vity IV (Tues. PM/Wed. M?): Single- photon interference. F (1) HeNe laser H G (2) (1) B G I Blue laser 1. Place the collimator and fiber, and align it so that the beam enters the collimator. Op4onally, place a straight plate guide to translate the collimator into alignment. You should not need to align it ver4cally. Otherwise it is not a good sign. Place also the filter in front of the fiber. 2. lign the second collimator in the second output of the interferometer. This second detector is nice but not cri4cal. 17

18 c4vity IV (Tues. PM/Wed. M): Single- photon interference. (4) HeNe laser (5) DC F DB B D Blue laser 4. Block the HeNe laser, turn the electronics and look for coincidences. 5. Do piezo scans with labview program Mdyn2015i or MDynrduino15 (depending on setup). The aim is for fringes in the coincidences to reach near zero- count minima. 6. DB and DC should show complementary fringes. 18

19 c4vity V (Wednesday M) Waveplates Goals: To learn how to align and set up waveplates. Materials: Hardware: Thompson polarizers (T) Polarizing beam splirer (N) 2 half- wave plates M on a rota4on mounts (best if they have an adjustable zero sekng). 19

20 c4vity V (Wed. M): Sekng up waveplates. (1) calibra4ng polarizer methods (1) PBS 57 (2) T (3) PBD 1. Set a polarizer with its transmission axis horizontal. Calibrate the polarizer using: polarizing beam splirer (PBS), Thompson prism (T), polarizing beam displacer (PBD) or Brewster reflec4on of glass prism. 2. Insert a second polarizer with its transmission axis ver4cal so no light is transmired. 3. Insert the half- wave plate in between the polarizers. When the axis of the waveplate is aligned with either polarizer (it does not marer which), there should be no light transmirer through the second polarizer. 4. Use this method to find the axes of both waveplates. 20

21 c4vity VI (Wednesday M, PM) Quantum eraser Goals: To learn how to setup and take data on the quantum eraser. Materials: Hardware: Interferometer from c4vity IV. 2 waveplates M and one polarizer N from c4vity IV. The polarizer should be oriented 45 degrees from horizontal. Plate- guide P to posi4on the polarizer in the dark. 21

22 c4vity VI (Wed.M): Quantum Eraser. DC HeNe laser (4) (5) F B (1) (3,4,5) DB D Blue laser 1. Place waveplates in each arm of the interferometer. 2. Redo the white- light fringes adjustment. 3. Do a piezo scan. It should show high- visibility fringes. 4. Rotate one of the waveplates by 45 degrees. Redo the scan. It should show no fringes. 5. Place the polarizer (N) 4lted 45 degrees aber the interferometer. Redo the scan. Fringes in DB should reappear at half the amplitude. 22

23 c4vity VII (Wednesday PM, Thursday M) Entanglement and Bell Goals: To learn how to setup an entangled state To measure nonlocal correla4ons To do a measurement of a Bell inequality Materials: Hardware: Setup from c4vity II, but with two- crystal BBO (X2) 2 waveplates (M) Polarizers N and T set to transmit horizontal polariza4on. Half- wave plate for blue laser V. Compensa4ng quartz crystal U. 23

24 c4vity VII (Wed. PM): Entanglement. F Blue laser (1) V (6) U (2) HeNe laser X2 D (5) (4) M (3) T 1. Setup for symmetric 3- degree parametric down- conversion. lignment should be similar to ac4vity II. lterna4vely, you can keep previous non- symmetric breadboard alignment. 2. Crystal X2 is a pair of type- I crystals 0.6 mm in thickness (each) but rotated 90 degrees to each other. 3. Place polarizers N and T before the filters. 4. Place zero- order half waveplates M before the polarizers. 5. Place zero- order half waveplate V (for 405 nm) before the crystals. 6. Place compensa4ng crystal U before the down- conversion crystal. 3 3 (4) M (3) N DB 24

25 c4vity VII (Wed. PM): Entanglement, cont. F Blue laser (7) V (8,11) U (10) HeNe laser 2 (10) (9,10,11) 7. Rotate pump polariza4on to 45- degrees with HWP (to 22.5 deg). 8. Compensa4ng crystal axis should be aligned the same as the second down- conversion crystal of the pair. If not known (common), guess. 9. Polarizers should be fixed. The HWP- polarizer pair are to be set up so that the act as a rota4ng polarizer (remember that HWP rotates at twice the angle). 10. Measure coincidences and 4lt the crystal pair so that: HH and VV should be maximum (and ~ equal). Hor(vert) 4lt for VV(HH). HV and VY should be a minimum (ideally zero) 11. Tilt the compensa4ng crystal so that: DD and are maximum (as much as HH or VV) D and D must be minumum (ideally zero) if no success, then rotate 25 U 90 degrees about its axis. 3 3 (9,10,11) 1

26 c4vity VII (Wed. PM/Thur. M): CHSH Bell viola4on. F Blue laser (7) HWP (10) (8,11) CC (10) HeNe laser 1. Understand the table on the right. 2. Take data by moving the two half- wave plates. 3. Do the calcula4on using the spreadsheet provided. 3 3 (9,10,11) (9,10,11) # State Pol- Hwp- Pol-B Hwp-B Coinc 1 a',b a',b a'+,b a'+,b a',b' a',b' a'+,b' a'+,b' a,b a,b a+,b a+,b a,b' a,b' a+,b' a+,b'

27 c4vity VIII (no 4me) Biphoton interference Goals: Perform yet a new type of interference where two photons act as one: the biphoton. Materials: Hardware: Interferometer setup per ac4vity IV 2 irises Polarizer N Polarizer T 27

28 c4vity VIII (Thur. M if 4me): Bonus- Biphoton interference. F (1) HeNe laser (2) B (3) (3) Blue laser 1. HeNe beam must go through the interferometer and through the fiber. Make sure that the interferometer is well aligned. 2. Place a beam splirer and a second collimator aber the interferometer so that the output of the interferometer goes into two fibers. Good alignment is very important. 3. Place two irises very accurately so that you can define the path of the HeNe beam VERY WELL. 28

29 c4vity VIII (Thur. M if 4me): Biphoton interference, cont. (5) (2) HeNe laser (1) (2) (3) (4) (3) F P H or SPF P V or LPF Blue laser 1. Replace mirror B for a flipper mirror, preferably over a transla4on stage and retrace the path through the irises. 2. Block the HeNe beam, flip the mirror and steer the blue beam through the irises and into the collimators. 3. Place two crossed Glan- Thompson polarizers before and aber the crystal. lterna4vely, put a short- pass and long- pass filters before and aber the crystal, respec4vely. This is so that the Blue beam produces down- conversion. ber the crystal the blue beam is blocked but the down- conversion photons are allowed through. 4. Rotate and 4lt the crystal by degrees so that it will produce down conversions for the new path. 5. Op4onal third collimator can be added aber the second port of the 29 interferometer. lignment of this is cri4cal.

30 c4vity VIII (Thur. M if 4me): Biphoton interference, cont. C (2) HeNe laser B F Blue laser 1. Data is taken by recording the coincidences between and B, and/or and C. a), B or C fringes alone are sinusoidal. b) B fringes have sharp peak but flat borom. c) C fringes are sinusoidal but have twice the frequency. 30