We propose two schemes for the implementation of quantum discrete Fourier transform in the ion trap system. In each scheme we design a tunable two-qubit phase gate as the main ingredient. The experimental implementation of the schemes would be an important step toward complex quantum computation in the ion trap system.
Based on the iSWAP gate generated from the XY interaction between solid-state qubits, we present an efficient quantum circuit for the implementation of discrete quantum Fourier transform. The relatively cumbersome and expensive controlled- R k gate and SWAP gate operations required for implementing discrete quantum Fourier transform in the naive quantum circuit are replaced only by iSWAP gate operation. The scheme can be realized using any physical system with XY interaction and it would be a useful step towards the implementation of more complex quantum computation in solid-state qubits.
We propose a simplified mathematical construction of the quantum Fourier transform which is suited for systems described by Ising-type Hamiltonians. By contrast to the standard Cooley-Tuckey scheme, which prescribes sequences of CPHASE gates, our implementation is based on one-qubit gates and a free evolution process. We also show how to obtain a quadratic speed-up by applying the conditional interactions simultaneously. Thus rather than O(N2) our implementation time scales as O(N). Finally, we show a realization of our method with homogeneous microwave driven ion traps in a magnetic field with gradient.
We propose an implementation of the quantum fast Fourier transform algorithm in an entangled system of multilevel atoms. The Fourier transform occurs naturally in the unitary time evolution of energy eigenstates and is used to define an alternative wave-packet basis for quantum information in the atom. A change of basis from energy levels to wave packets amounts to a discrete quantum Fourier transform within each atom. The algorithm then reduces to a series of conditional phase transforms between two entangled atoms in mixed energy and wave-packet bases. We show how to implement such transforms using wave-packet control of the internal states of the ions in the linear ion-trap scheme for quantum computing.