Researchers have devised a quantum information processing system based on nuclear spin1.
The researchers studied the nuclear spins of several organic molecules using NMR, showing that it is possible to process information by tapping into the spins of atomic nuclei. This opens up the possibility of designing a quantum register, a memory device to be used in future quantum computers.
Unlike classical computation, which encodes messages in classical bits (0 or 1), quantum computation encodes messages in quantum bits or 'qubits'. A qubit can be 0, 1, or a superposition of both.
Nuclei of all atoms comprising neutrons and protons have the quantum property of spin, which is the intrinsic angular momentum of a single particle. The qubit here is spin, which acts as tiny magnet. When placed inside a magnetic field, this tiny magnet has two extreme possibilities — 'parallel' or 'anti-parallel' to the applied magnetic field. Researchers denoted the parallel and anti-parallel states as 0 and 1, respectively.
To study the quantum information processing potential of nuclear spins, the researchers took several organic molecules — 5-bromothiophene-2-carbaldehyde for a two-qubit register, acrylonitrile for a three-qubit register and aspirin for a four-qubit register — and used them in an NMR spectrometer.
The researchers were able to prepare a singlet state that has much longer lifetime than all other states. The singlet state of a pair of spin-half particles is a special quantum state with zero spin. The researchers created a spin lock using radiofrequency pulses, which is necessary to preserve the singlet state until the information is processed.
"This work on the initialization of quantum registers is the first application of long-lived states for quantum information processing," says lead researcher Thirthahalli Mahesh. This technique could also be used in an optics-based quantum information processor, he adds.
