Recently, Murani et al. [1] questioned the existence ofthe dissipative quantum phase transition (DQPT) in a singleJosephson junction (JJ) predicted nearly 40 years ago [2,3].This conclusion is based on misperception of the principlesunderlying the DQPT theory.First, we recall in a nutshell the basics of the DQPTtheory. The DQPT is a joint effect of Coulomb interaction,dissipation, and quantum mechanics. The Coulomb blockade makes the JJ an insulator at small bias. However, it iseffective only if the Coulomb energy EC ～ e2=C exceedsthe quantum-mechanical uncertainty ?=τ, where τ ? RsC isthe time of the charge relaxation in the circuit. Here, C isthe capacitance of the JJ, and Rs is the shunt resistance. Thecondition EC ～ ?=τ agrees with the condition Rs ? Rq,where the DQPT was predicted [2,3] (the dashed line inFig. 1). Here, Rq ? h=4e2 is the quantum resistance. Theexistence of the DQPT has been supported by experimentalwork [4–9], and possible applications for qubits have beendiscussed [10].
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