The universal CNOT quantum gate developed by Ahn has a qubit which is represented by a state from among polarized intervalley states of an electron in aquantum dot. This allows the number of quantum dots necessary for a qubit operation to be reduced by half compared with the qubit using electron spins. Moreover, in one example, substantially all the qubit operation using the polarized intervalley states were electrically controlled. Also, compared with a qubit derived from using electron spins, which requires both static and dynamic magnetic fields, it may be easier to control quantum states of an electron in a quantum dot
Quantum gate operation of the spin qubits may utilize the Heisenberg interaction or the exchange interaction. It is well known that the Heisenberg interaction alone may not provide a universal quantum gate because it has too much symmetry. Moreover, in order to control the Heisenberg interaction in quantum dots, both static and dynamic magnetic fields are likely required. Therefore, implementation is needed such that a single physical state can possibly constitute one logical qubit with a universal gate operation that is substantially electrically controlled.
FIG. 1 is a diagram showing an illustrative embodiment of a universal controlled NOT (CNOT) quantum gate