Editing Homodyne detection (section)

==Applications==
[[Lock-in amplifier]]s are homodyne detectors integrated into measurement equipment or packaged as stand-alone laboratory equipment for sensitive detection and highly selective filtering of weak or noisy signals. Homodyne/lock-in detection has been one of the most commonly used signal processing methods across a wide range of experimental disciplines for decades.

Homodyne and heterodyne techniques are commonly used in [[Time-domain thermoreflectance|thermoreflectance]] techniques.

In the processing of signals in some applications of [[magnetic resonance imaging]], homodyne detection can offer advantages over magnitude detection. The homodyne technique can suppress excessive noise and undesired quadrature components (90° out-of-phase), and provide stable access to information that may be encoded into the [[Phase (waves)|phase or polarity]] of images.<ref name="NollNishimura1991">{{cite journal |last1=Noll |first1=D. C. |last2=Nishimura |first2=D. G. |last3=Macovski |first3=A. |title=Homodyne detection in magnetic resonance imaging |journal=IEEE Transactions on Medical Imaging |volume=10 |issue=2 |year=1991 |pages=154–163 |issn=0278-0062 |doi=10.1109/42.79473|pmid=18222812 }}</ref>

Homodyne detection was one of the key techniques in demonstrating [[quantum entanglement]].<ref>{{Cite journal |journal=Nature Communications |title=Experimental proof of nonlocal wavefunction collapse for a single particle using homodyne measurements |author1=Maria Fuwa |author2=Shuntaro Takeda |author3=Marcin Zwierz |author4=Howard M. Wiseman |author5=Akira Furusawa |volume=6 |number=6665 |date=24 March 2015 |doi=10.1038/ncomms7665 |pages=6665 |arxiv = 1412.7790 |bibcode = 2015NatCo...6E6665F |pmid=25801071}}</ref> This has led to the possibility of providing a room temperature [[quantum sensor]] with [[continuous-variable quantum information]].<ref name=":0">{{cite arXiv |last1=Gurses |first1=Volkan |title=Free-space quantum information platform on a chip |date=2024-06-13 |eprint=2406.09158 |last2=Davis |first2=Samantha I. |last3=Sinclair |first3=Neil |last4=Spiropulu |first4=Maria |last5=Hajimiri |first5=Ali|class=quant-ph }}</ref> However, challenges include reducing noise, increasing bandwidth and improving the integration of electronic and photonic components.<ref>{{Cite journal |author1=JOEL F. TASKER |author2=JONATHAN FRAZER |author3=Giacomo Ferranti |author4=JONATHAN C. F. MATTHEWS |date=17 May 2024 |title=A Bi-CMOS electronic photonic integrated circuit quantum light detector |journal=Science Advances |volume=10 |arxiv=2305.08990 |doi=10.1126/sciadv.adk6890 |number=20|pages=eadk6890 |pmid=38758789 |pmc=11100555 |bibcode=2024SciA...10K6890T }}</ref> Recently, these challenges have been overcome to demonstrate a free-space-coupled room temperature quantum sensor with large-scale integrated photonics and electronics.<ref name=":0" />

An [[Encryption|encrypted]] [[secure communication]] system can be based on [[quantum key distribution]] (QKD). An efficient receiver scheme for implementing QKD is balanced homodyne detection (BHD) using a positive–intrinsic–negative ([[PIN diode|PIN]]) diode.<ref name=Xu/>