Quantum logic

Research on multi-qubit molecules starts with the synthesis and characterization of systems that seem to embody more than one qubit, for example, systems with weakly coupled electron spins. Indeed, many molecular structures include several weakly coupled magnetic ions [76-78]. On a smaller scale, the capability of implementing a Controlled-NOT quantum logic gate using molecular clusters... 

Figure 7.3 Schematic representation of the operations of some quantum logic gates acting on two qubits. In quantum computation, single qubit rotations (Figure 7.2) and CNOT (controlled-NOT) or INSWAP quantum gates are universal.

Furthermore, we have shown in Refs. [28, 112] that in mulfiqubit quantum computation, it is vital to consider all possible modulations and fields, and not only those that directly perform a quantum logic gate. Thus, while usually one only requires the optimization of the fields applied to perform the gate, we have stressed that the gate fidelity can be greatly increased if one also applies and optimizes all other possible fields. 

SLI is not specific to molecular eigenstates, but universal to the superposition of any eigenstates in a variety of quantum systems. It is thus expected as a new tool for quantum logic gates not only in MEIP but also for other systems such as atoms, ions, and quantum dots. SLI also provides a new method to manipulate WPs with fs laser pulses in general applications of coherent control. 

A quantum computational network can be decomposed into quantum logic gates [94, 95], analogously to the situation for classical computers. Quantum logic gates provide fundamental examples of conditional quantum dynamics, in which one subsystem undergoes a coherent evolution, which depends on the quantum state of another subsystem. 

Gershenfeld and Chuang s two-qubit system [101] uses an NMR machine and the protons in 25. They demonstrated a nonlinear interaction between spins, a prerequisite for quantum logic gates. This was realized through the controlled-NOT operation (CNOT) which conditionally flips one spin based on the value of another [102], This gate can be considered as a quantum XOR gate. 

Extraction of information from the register—in a sense, cashing in your chips — would be associated with collapse of the wavefunction to one of its components (), with a probability a,p. A quantum logic operation pcriormod on the input... 

Bonding Patterns that Neutral and Charged Gold Clusters form with Small Ammonia Clusters and which implement Quantum Logic Gates... 

QUANTUM LOGICS BASED ON FOUR-PHOTON ENTANGLEMENT... 

Quantum logics based on four-photon entanglement... 

Thus far, studies of coherent optical processes in a PBG have assumed fixed (static) values of the atomic transition frequency [Quang 1997], However, in order to operate quantum logic gates, based on pairwise entanglement of atoms by field-induced dipole-dipole interactions [Brennen 1999 Petrosyan 2002 Opatrny 2003], one should be able to switch the interaction on- and off-, most conveniently by AC Stark-shifts of the transition frequency of one atom relative to the other, thereby changing its detuning from the PBG edge. 

Here, we rq>ort related trapped-ion research at NIST on (1) the study of the dynamics of a two-level atomic system coupled to harmonic atomic motion, (2) the creation and characterization of nonclassical states of motion such as Schrodinger-cat superposition states, and (3) quantum logic for the generation of highly entangled states and for the investigation of scaling in a quantum computer. 

The key to making a quantum logic gate is to provide conditional dynamics that is, we desire to perform on one physical subsystem a unitary transformation which is conditioned upon the quantum state of another subsystem [46]. In the context of cavity QED, the required conditional dynamics at the quantum level has recently been demonstrated [50,51]. For trapped ions, conditional dynamics at the quantum level has been demonstrated in verifications of zero-point laser cooling where absorption on the red sideband depended on the motional quantum state of the ion [11,12]. Recently, we have demonstrated a CN logic gate in this experiment, we also had the ability to prepare arbitrary input states to the gate (the keyboard operation of step (2a) below). 

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