Method for determining a spin/charge conversion operating point, method for determining an operating point associated with charging of a singlet state and system therefor

A method for determining an optimal spin/charge conversion operating point in a system comprising a pair of quantum dots comprising a first quantum dot and a second quantum dot, the pair of quantum dots containing two charged particles and adopting a first charge state {2,0} in which both charged particles are in the first quantum dot, a second charge state {1,1} in which each quantum dot contains a charged particle, or a third charge state {0,2} in which both charged particles are in the second quantum dot, the charge state being a function of the voltage applied to at least two gates configured to modulate a charge state of the pair of quantum dots, the value of the voltages defining an operating point of the pair of quantum dots;

• the charged particles adopting a first spin state, referred to as the singlet spin state S, or a second spin state, referred to as the triplet spin state among the triplet spin state T0 or the triplet spin state T+/T−, the method comprising:
• a step of determining an operating point associated with two charged particles being in the singlet spin state S in the pair of quantum dots;
• and, for each of a plurality of conversion operating points:
• a step 4E1 of initialising the system in the singlet spin state S with the operating point associated with the two charged particles being in the singlet state S in the pair of quantum dots, the operating point at the end of the initialisation step being associated with the first charge state {2,0};
• a step 4E2 of spin/charge converting the charge state of the system using the conversion operating point considered;
• a step 4E3 of measuring the signal using a charge state detector comprising an electrometer for the charge state thus converted;
• and
• a step 4E4 of initialising the system in a spin state that can assume either the singlet state S or the triplet state TO or T+/T− according to a set probability, referred to as the mixed spin state, using the operating point associated with the two charged particles being in the singlet state in the pair of quantum dots;
• a step 4E5 of spin/charge converting the charge state of the system using the conversion operating point considered so as to obtain a mixed charge state;
• a step 4E6 of measuring the signal measured by the charge state detector for the mixed charge state thus converted;
• a step 4E7 of determining the difference between the signal measured for the charge state associated with the singlet spin state and the signal measured for the charge state associated with the mixed spin state;
• both measurement steps 4E3 and 4E6 being carried out at an operating point associated with a fully isolated regime in which, for a reference duration, no exchange of charged particles is possible between the first quantum dot and the second quantum dot, the reference duration being greater than or equal to the time required for the implementation of the measurement step, the preceding steps 4E1-4E7 being repeated a plurality of times for each conversion operating point among the plurality of operating points so as to establish a difference between the signal associated with the singlet state and the signal associated with the mixed state, the conversion operating point for obtaining the highest difference being considered as the optimal spin/charge conversion operating point.