# Presentation: 016834

## New Technologies for High-efficiency DetectorsP. Kwiat, D. James, A. VanDevender 

- MURI (2003)

## Outline

- 1.  The trouble with IR detectors
- 2.  Quantum transducer  high  detector
- 3.  Photon-counting ultra-high  detector in
- 	atomic vapor

## (Undesirable) Characteristics of (InGaAs) IR detectors

- Low efficiencies (~10-20%)
- High dark counts (10-100,000 s-1 *)
- Require cryogenic cooling (150-250K)
- High afterpulsing probability
- Future production uncertain
- * Can be reduced by gating (10-4 - 10-3 s-1)

## Quantum Transducer

**Capitalize on high-efficiency low-noise single-photon counters (Si APDs) from 500-800nm**
**Convert from (telecom) flying qubit to (atomic) storage qubit**

- Example:

## Phase-matching in Periodically-poled LiNbO3

- Momentum conservation:  ****in + ****escort + ****PPLN = out
-  = 2 ’= 2n()/c;          PPLN = 2 = poling period

- Conversion probability ~ sin2( Eescort LPPLN)
- 			= sin2(√Iescort LPPLN)

- Phase-matching in Periodically-poled LiNbO3

- “Rabi” oscillations

## Preliminary results

**Linear output for varying       1550nm input power **
**(non-deletion limit)**

**Recently observed operation at single-photon level; **
**	****current background level is <3 x 10****-4****/pulse**

**Partial Rabi oscillation observed with varying 1064 nm power**

## Effect of pulse shape

**Conversion system tested with cw 1550 nm source ******** averaged ****	****conversion efficiency ~70% per FWHM escort pulsewidth**
**Next step: use optimized 1550 nm pulse (~300ps) ******** **
**	****	****	****	****	****           ****>98% conversion efficiency**

**?**

## Quantum Transducer – Transforming a qubit

- “Observation of Quantum Frequency Conversion”                             Huang and Kumar, PRL **68**, 2153 (1992) – demonstrated preservation of nonclassical intensity correlations through upconversion

*** **The reverse process has successfully been used to produce high-quality entangled photon pairs PGK et al., PRA **65**, 012301 (1999); see also Kim, Kulik, and Shih, PRL **86**, 1370 (2001)

## Atomic Vapor-based High-efficiency Distinguishing Single-Photon Detector

**Atomic Vapor-based High-efficiency ****Distinguishing Single-Photon Detector**

- D. James and PGK, PRL **89**, 183601 (2002)
- A. Imamoglu, PRL **89**, 163602 (2002)
**R. Cook, Patent 5,095,212 (1992)**

## Vapor Cell Detector

** ****Look for multiple photons emitted per excited atom ******** ******** > 99%**
** ****Image the light ******** count the number of atoms ******** distinguish incident photon number (maybe up to n~ 50)**
** ****Problems with “dark counts” under investigation**
** ****Requires narrow linewidth, special ******** (combine with upconversion technique)**

- D. James and PGK, PRL **89**, 183601 (2002)

## Summary

- Demonstrated 1550nm + 1064nm  631nm conversion, using pulsed Nd:YAG and cw 1550nm
- 	 ~ 70% observed  max ~90±5% (for pulsed 1550nm)
- Still need to reduce background (currently <10-3/pulse)
- Coherent transduction  conversion of arbitrary qubit
- Atomic-vapor scheme allows ultra-high efficiency photon-number resolving detection
-   up to 99.8%, imaging detector might distinguish up to 50 photons
- Noise might be a problem....work in progress

- _Summary_