Calibration of particle detectors

1. A method of calibrating a first optical detector arrangement comprising:

simultaneously generating a plurality of entangled photon pairs, such that one photon from each pair traverses a first path and the other photon from each pair traverses a second path;

using the first optical detector arrangement to calculate a number of photons received along the first path;

using a second optical detector arrangement to calculate a number of simultaneously generated photons received along the second path; and

using the calculated numbers of simultaneously generated photons having arrived along the first and second paths to calculate an estimate of the detection efficiency of the first optical detector arrangement by determining joint count statistics for the first and second detector arrangements and using the joint count statistics to calculate the estimate of the detection efficiency of the first optical detector arrangement.

2. The method of claim 1 further comprising generating the plurality of entangled photon pairs by spontaneous parametric down-conversion.

3. The method of claim 2 further comprising using a light source selected from the group consisting of: non-linear crystals, optical fibers, periodically poled waveguides and atomic gases.

4. The method of claim 2 further comprising using a light source comprising a potassium dihydrogen phosphate crystal pumped by a Ti:Sapphire laser.

5. The method of claim 1 further comprising calculating the estimate of the detection efficiency of the first optical detector arrangement by minimizing a difference between measured outcome statistics comprising the calculated numbers of simultaneously generated photons and predicted outcome statistics, using a least-squares estimation.

6. The method of claim 5 further comprising using the Frobenius norm as a distance measure, with the detection efficiency of the first optical detector arrangements, the detection efficiency of the second optical detector arrangement, and state coefficients as free parameters, subject to normalization and physicality conditions.

7. The method of claim 1 wherein the first detector arrangement comprises a channel, the method further comprising estimating the transmission efficiency of the channel.

8. A method of calibrating a first optical detector arrangement comprising:

simultaneously generating a plurality of entangled photon pairs, such that one photon from each pair traverses a first path and the other photon from each pair traverses a second path;

using the first optical detector arrangement to calculate a number of photons received along the first path;

using a second optical detector arrangement to calculate a number of simultaneously generated photons received along the second path;

using the calculated numbers of simultaneously generated photons having arrived along the first and second paths to calculate an estimate of the detection efficiency of the first optical detector arrangement; and

using the calculated numbers of simultaneously generated photons having arrived along the first and second paths to calculate an estimate of the detection efficiency of the second detector arrangement.

9. The method of claim 8 further comprising generating the plurality of entangled photon pairs by spontaneous parametric down-conversion.

10. The method of claim 9 further comprising using a light source selected from the group consisting of: non-linear crystals, optical fibers, periodically poled waveguides and atomic gases.

11. The method of claim 9 further comprising using a light source comprising a potassium dihydrogen phosphate crystal pumped by a Ti:Sapphire laser.

12. The method of claim 8 further comprising calculating the estimate of the detection efficiency of the first optical detector arrangement by minimizing a difference between measured outcome statistics comprising the calculated numbers of simultaneously generated photons and predicted outcome statistics, using a least-squares estimation.

13. The method of claim 12 further comprising using the Frobenius norm as a distance measure, with the detection efficiency of the first optical detector arrangements, the detection efficiency of the second optical detector arrangement, and state coefficients as free parameters, subject to normalization and physicality conditions.

14. The method of claim 8 wherein the first detector arrangement comprises a channel, the method further comprising estimating the transmission efficiency of the channel.

15. Apparatus comprising:

a light source arranged to simultaneously generate a plurality of entangled photon pairs, such that one photon from each pair traverses a first path and the other photon from each pair traverses a second path;

a first detector arrangement for calculating a number of photons received along the first path;

a second detector arrangement for calculating a number of simultaneously generated photons received along the second path; and

logic for calculating an estimate of the detection efficiency of the first detector arrangement using the calculated numbers of simultaneously generated photons having arrived along the first and second paths by determining joint count statistics for the first and second detector arrangements and using the joint count statistics to calculate the estimate of the detection efficiency of the first optical detector arrangement.

16. The apparatus of claim 15 wherein the light source comprises a potassium dihydrogen phosphate crystal arranged to be pumped by a Ti:Sapphire laser.

17. The apparatus of claim 15 further comprising logic for calculating the estimate of the detection efficiency of the first optical detector arrangement by minimizing a difference between measured outcome statistics comprising the calculated numbers of simultaneously generated photons and predicted outcome statistics, using a least-squares estimation, and using the Frobenius norm as a distance measure, with the detection efficiency of the first optical detector arrangements, the detection efficiency of the second optical detector arrangement, and state coefficients as free parameters, subject to normalization and physicality conditions.

18. The apparatus of claim 15 wherein the first detector arrangement comprises a channel, and the apparatus comprises logic for estimating the transmission efficiency of the channel.

19. Apparatus comprising:

a light source arranged to simultaneously generate a plurality of entangled photon pairs, such that one photon from each pair traverses a first path and the other photon from each pair traverses a second path;

a first detector arrangement for calculating a number of photons received along the first path;

a second detector arrangement for calculating a number of simultaneously generated photons received along the second path;

logic for calculating an estimate of the detection efficiency of the first detector arrangement using the calculated numbers of simultaneously generated photons having arrived along the first and second paths; and

logic for using the calculated numbers of simultaneously generated photons having arrived along the first and second paths to calculate an estimate of the detection efficiency of the second detector arrangement.

20. The apparatus of claim 19 wherein the light source comprises a potassium dihydrogen phosphate crystal arranged to be pumped by a Ti:Sapphire laser.

21. The apparatus of claim 19 further comprising logic for calculating the estimate of the detection efficiency of the first optical detector arrangement by minimizing a difference between measured outcome statistics comprising the calculated numbers of simultaneously generated photons and predicted outcome statistics, using a least-squares estimation, and using the Frobenius norm as a distance measure, with the detection efficiency of the first optical detector arrangements, the detection efficiency of the second optical detector arrangement, and state coefficients as free parameters, subject to normalization and physicality conditions.

22. The apparatus of claim 19 wherein the first detector arrangement comprises a channel, and the apparatus comprises logic for estimating the transmission efficiency of the channel.

23. A non-transitory computer-readable medium containing computer instructions stored therein for calibrating an optical detector arrangement by:

receiving data representing a calculated number of photons received along a first path;

receiving data representing a calculated number of simultaneously generated photons received along a second path; and

calculating an estimate of the detection efficiency of a detector arrangement detecting photons in the first path using the calculated numbers of simultaneously generated photons having arrived along the first and second paths by determining joint count statistics for the first and second detector arrangements and using the joint count statistics to calculate the estimate of the detection efficiency of the first optical detector arrangement.

24. The non-transitory computer-readable medium of claim 23 containing computer instructions stored therein for storing, or displaying, or communicating electronically, the estimate of the detection efficiency of the first optical detector arrangement.

25. A non-transitory computer-readable medium containing computer instructions stored therein for calibrating an optical detector arrangement by:

receiving data representing a calculated number of photons received along a first path;

receiving data representing a calculated number of simultaneously generated photons received along a second path;

calculating an estimate of the detection efficiency of a first detector arrangement detecting photons in the first path using the calculated numbers of simultaneously generated photons having arrived along the first and second paths; and

calculating an estimate of the detection efficiency of a second detector arrangement detecting photons in the second path using the calculated numbers of simultaneously generated photons having arrived along the first and second paths.

26. The non-transitory computer-readable medium of claim 25 containing computer instructions stored therein for storing, or displaying, or communicating electronically, the estimates of the detection efficiencies of the first and second optical detector arrangement.