RESEARCH HIGHLIGHTS
Photonics In the crossfire
The elimination of detrimental cross-talks in single-photon detectors pushes quantum optics to new limits
Light and electric current can both be used for computing, albeit with key differences. Whereas conventional computers do logic through the movement of electrons, newer and faster computers called quantum computers perform the same job using single particles of light, known as photons. The use of photons, however, is not without its problems. One major obstacle has been the limited capability of photon detec- tors to reliably count the number of photons in a light beam. Dmitry Kalashnikov at the A*STAR Data Storage Institute and co-workers have now proposed a scheme to improve the counting precision of photon detectors1
.
The performance of most photon detectors is limited due to the inherent difficulties involved in detecting tiny signals caused by the absorption of single photons. One way to overcome this problem is to use an ‘avalanche’ photon detector, in which a single photon triggers an amplified number of electrons in the device through the process of avalanche multiplication. Several hundreds of these detectors can be packed into an array to form a multi-photon pixel counter (MPPC) (see image). However, MPPCs also have their limitations. “A significant
drawback for MPPC is cross-talk. When an MPPC detects a photon, the electrical avalanche is accompanied by the emission of secondary photons, which cause signals in neighboring pixels,” says Kalashnikov. In order to ‘filter out’ this cross-talk, the researchers developed a method to determine the average cross- talk for an MPPC. The average value can then be subtracted from future experiments. In one experiment, the researchers directed a weak laser beam
at the MPPC. Based on known properties of photons in the laser, they were able to determine the cross-talk probability of the MPPC. In another experiment, the researchers used entan- gled photons instead of conventional light. Entangled photons form the basis of many quantum computing applications, and they induce a different MPPC response. Comparing the two experiments therefore allows a clear distinction between cross-talk effects caused by regular photons and those caused by entangled photons. Most of the undesired crosstalk can be eliminated in this way, and enables
A*STAR RESEARCH OCTOBER 2011– MARCH 2012 An MPPC detector consisting of an array of avalanche photodiodes
a considerably more precise method of counting photons from quantum sources. “Multi-photon pixel counters are widely used in quantum optics, quantum computing and quantum cryptog- raphy,” says Kalashnikov. “Moreover, they are extensively used in high-energy physics applications, such as the photosensors in scintillator detectors.” The new MPPC counting method may be beneficial in a vast number of experiments involving the study of atomic–photon interfaces, as well as innovative applica- tions in astronomy.
■
1. Kalashnikov, D. A., Tan, S. H., Chekhova, M. V. & Krivitsky, L. A. Accessing photon bunching with a photon number resolving multi-pixel detector. Optics Express 19, 9352–9362 (2011).
51
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96