▁of ▁Quant um ▁information ▁science . ▁ ▁In ▁general , ▁it ▁is ▁easy ▁to ▁vary ▁the ▁phase ▁gained ▁by ▁the ▁phot on ▁between ▁the ▁two ▁paths , ▁for ▁example ▁by ▁stretch ing ▁the ▁fi ber , ▁while ▁it ▁is ▁much ▁more ▁difficult ▁to ▁vary ▁the ▁amplit udes ▁which ▁are ▁therefore ▁fixed , ▁typically ▁at ▁ 5 0 %. ▁The ▁created ▁qu bit ▁is ▁then ▁▁▁▁ ▁which ▁covers ▁only ▁a ▁subset ▁of ▁all ▁possible ▁qu bits . ▁ ▁Me asure ment ▁in ▁the ▁{ , } ▁basis ▁is ▁done ▁by ▁meas uring ▁the ▁time ▁of ▁arrival ▁of ▁the ▁phot on . ▁ ▁Me asure ment ▁in ▁other ▁bases ▁can ▁be ▁achieved ▁by ▁letting ▁the ▁phot on ▁go ▁through ▁a ▁second ▁M Z ▁before ▁measurement , ▁though , ▁similar ▁to ▁the ▁state ▁prepar ation , ▁the ▁possible ▁measurement ▁set ups ▁are ▁restricted ▁to ▁only ▁a ▁small ▁subset ▁of ▁possible ▁qu bit ▁measurements . ▁ ▁Dec oh er ence ▁Time - bin ▁qu bits ▁do ▁not ▁suffer ▁from ▁dep olar ization ▁or ▁polar ization ▁mode - dis p ersion , ▁making ▁them ▁better ▁su ited ▁to ▁fi ber ▁opt ics ▁applications ▁than ▁polar ization ▁encoding . ▁Phot on ▁loss ▁is ▁easily ▁detect able ▁since ▁the ▁absence ▁of ▁phot ons ▁does ▁not ▁correspond ▁to ▁an ▁allowed ▁state , ▁making ▁it ▁better ▁su ited ▁than ▁a ▁phot on - number ▁based ▁encoding . ▁ ▁References ▁http :// ar xiv . org / abs / quant - ph / 0 2 0 5 1 4 4 ▁http :// ar