Simultaneous readout of two charge qubits

Jian Li*, Göran Johansson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We consider a system of two solid state charge qubits, coupled to a single readout device, consisting of a single-electron transistor (SET). The conductance of each tunnel junction is influenced by its neighboring qubit, and thus the current through the transistor is determined by the qubits' state. The full counting statistics of the electrons passing the transistor is calculated, and we discuss qubit dephasing, as well as the quantum efficiency of the readout. The current measurement is then compared to readout using real-time detection of the SET island's charge state. For the latter method we show that the quantum efficiency is always unity. Comparing the two methods a simple geometrical interpretation of the quantum efficiency of the current measurement appears. Finally, we note that full quantum efficiency in some cases can be achieved measuring the average charge of the SET island, in addition to the average current.

Original languageEnglish
Article number085312
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number8
StatePublished - 9 Feb 2007
Externally publishedYes


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