Abstract Time reversal and spin flip are discrete symmetry operations of substantial importance to quantum information and quantum computation. Spin flip arises in the context of separability, quantification of entanglement and the construction of universal NOT gates. The present work investigates the relationship between the quantum state of a multiqubit system represented by the discrete Wigner function (DWFs) and its spin-flipped counterpart. The two are shown to be related through a Hadamard matrix that is independent of the choice of the quantum net used for the tomographic reconstruction of the DWF. These results are of interest to cases involving the direct tomographic reconstruction of the DWF from experimental data, and in the analysis of entanglement related properties purely in terms of the DWF.
Quantum computing (QC) is a radically new approach to computation. Classical computing is based on the idea of bits: strings of 1's and 0's on which we do arithmetic operations. QC, however, is based on quantum bits, qubits, and new physical operations. Despite the complexity of QC, we contend that it is an appropriate and useful topic for undergraduate physics students. In this talk, we present our results from three small QC projects relating to flipping coins. In the first, we investigate the results of a secret coin flip and use QC to guess whether the coin landed on heads or tails. In the second, we determine whether a given coin is fair or unfair using only a single qubit ( instead of multiple bits). In the third, we explore how quantum communication can alleviate dishonest player biases in coin flipping cryptographic primitives.
Abstract Impurities hosted in semiconducting solid matrices represent an extensively studied platform for quantum computing applications. In this scenario, the so-called flip-flop qubit emerges as a convenient choice for scalable implementations in silicon. Flip-flop qubits are realized implanting phosphorous donor in isotopically purified silicon, and encoding the logical states in the donor nuclear spin and in its bound electron. Electrically modulating the hyperfine interaction by applying a vertical electric field causes an Electron Dipole Spin Resonance (EDSR) transition between the states with antiparallel spins {∣↓⇑⟩,∣↑⇓⟩} {|↓⇑〉,|↑⇓〉} , that are chosen as the logical states. When two qubits are considered, the dipole-dipole interaction is exploited to establish long-range coupling between them. A universal set of quantum gates for flip-flop qubits is here proposed and the effect of a realistic 1/f noise on the gate fidelity is investigated for the single qubit Rz(−2π) Rz(−π2) and Hadamard gate and for the two-qubit iSWAP iSWAP gate.