Abstract
A central problem for implementing efficient quantum computing is how to realize fast operations (both one- and two-bit ones). However, this is difficult to achieve for a collection of qubits, especially for those separated far away, because the interbit coupling is usually much weaker than the intrabit coupling. Here we present an experimentally feasible method to effectively couple two flux qubits via a common inductance and treat both single and coupled flux qubits with more realistic models which include the loop inductance. The main advantage of our proposal is that a strong interbit coupling can be achieved using a small inductance, so that two-bit operations as fast as one-bit ones can be easily realized. We also show the flux dependence of the transitions between states for the coupled flux qubits.
Highlights
We find the interesting result that ⌬͑Lis almost flat at f = 0.5 (0.011Ͻ ⌬͑L / EJ Ͻ 0.0135) when 0 ഛ L ഛ 0.85 These features indicate that, even with a large loop inductance of L = 1, in the vicinity of f = 0.5 the two lowest eigenstatesdenoted by0͘ and1͘ for the ground and the first excited states, respectivelyremain suitable basis states for a flux qubit
For the charge qubits coupled by LC-oscillator modes[13] or by an inductance,[14] the inductances proposed to be used are ϳ3.6 H or ϳ30 nH, respectively, for a two-bit operation ten times slower than the typical one-bit operation
Because two-bit operations are much slower than one-bit operations in the inductively coupled charge qubits, an efficient scheme is required to minimize the number of two-bitas opposed to one-bitoperations to obtain a conditional gate.[14]
Summary
͑b Two flux qubits coupled by a common inductance Lc, where the external flux ⌽e is applied within the left loop cACh11͑ioLo=cBsCe12͑A␣i1=i.=CT0͑.hi8͒e, aEpnJadi3͒r=aEm␣JiieE=teJ3ir5s, Eaocnifd, ewCahc3͑hier=efl␣uEixCci͑q=i,ueb2wi/ti2thCareii=.E1TJo,i1͒2=i.mEHpJie2ler=emEewJniet, a readout of the flux-qubit states, a switchable superconducting flux transformer is employed to couple the dc-SQUID magnetometer with the inductance L inaor Lc inbduring the quantum measurement. This coupling is switched off in the absence of a readout
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