Yamamoto, NaokiNurdin, HendraJames, Matthew RPetersen, Ian2009-12-152010-12-202009-12-152010-12-20Physical Review A 78.4 (2008): 042339/1-111050-29471094-1622http://hdl.handle.net/10440/1010http://digitalcollections.anu.edu.au/handle/10440/1010In this paper, we consider a linear quantum network composed of two distantly separated cavities that are connected via a one-way optical field. When one of the cavities is damped and the other undamped, the overall cavity state obtains a large amount of entanglement in its quadratures. This entanglement, however, immediately decays and vanishes in a finite time. That is, entanglement sudden death occurs. We show that the direct measurement feedback method proposed by Wiseman can avoid this entanglement sudden death, and, further, enhance the entanglement. It is also shown that the entangled state under feedback control is robust against signal loss in a realistic detector, indicating the reliability of the proposed direct feedback method in practical situations.11 pageshttp://www.sherpa.ac.uk/romeo/index.php "Author can archive pre-print (ie pre-refereeing) … post-print (ie final draft post-refereeing) … [and] publisher's version/PDF. Link to publisher version … [and] Copyright notice required. Publisher's version/PDF can be used on … employers web site." - from SHERPA/RoMEO site (as at 25/02/10). ©2008 The American Physical SocietyKeywords: Control theory; Feedback control; Quantum optics; Robust control; State feedback; Direct feedbacks; Direct measurements; Entangled states; Finite times; Measurement feedbacks; Optical fields; Quantum networks; Realistic detectors; Signal losses; Sudden de2008-10-3110.1103/PhysRevA.78.0423392016-02-24