The Larmor precession panel allows the user to apply a magnetic field to the qubit and view the evolution of the qubit state.
The Rabi Field tab allows the user to see how the state of qubit is affected by two magnetic fields. The one rotates around the z-axis, on the x-y plane pointing towards the origin, and the second is a field the magnetic field along the z-axis that points from toward to the origin from Z+. There are three sliders on the tab when selecting the Rabi Field. Figure 3.17 shows the control tab on the simulator. The first slider is the Bz value which is the strength of the magnetic field that is along the z-axis. Adjusting this from low to high will make the qubit rotate around the z-axis at a faster pace. The second slider controls the strength of the perpendicular magnetic field that is rotating around the z-axis, along the x-y plane. Increasing the value of the slider will cause the qubit to rotate at a higher speed around the rotating magnetic field. This can be difficult to see if the magnetic field is rotating at a higher speed and also if the strength of the Bz is high (relatively speaking). The final slider controls the angular velocity (ω) for the Bperp magnetic field around the z-axis. This is measured in radians/second.
There is a check box that allows the simulator to match the speed of the rotation of the Bperp to the Larmor frequency. This is the frequency at which the combined force of Bperp and Bz are matched in such a way that the Bz pushes the qubit around the z-axis at the same speed of the Bperp magnetic field causing it to " ip" or move from the Z+ and Z- poles. When the user checks this check box, the simulator will calculate the correct value of ω and will change it correctly. If the Bz value is changed, the ω value will be updated accordingly. The last control does not affect the simulation of the Rabi Field, but it allows the user to view the path of the qubit, affected by the two magnetic fields. When the user clicks on the button "Show Trail", it will become depressed and the length of the trail, or previous states of the qubit will be shown. Because of computing constraints, the trail is limited and will continually follow the path of the qubit.
To start the effects of the Rabi field, click on the "Start" button. This will apply the two magnetic fields on only the visible qubits in the simulator. If the slider values are changed, they will take effect immediately. One this to note is that the effect of the magnetic fields is the change in the qubit from its original state. Changing the slider may cause the qubit(s) to move in a sudden or jerky motion. This is the because the the calculation of the current qubit state is the effect of the magnetic field with the spinor values applied from the start time to the current time. If there are problems viewing the trail of the spinor, it may be best to "hide" the trail of the qubit and then "show" it later after the spinor values have been set.
Lastly, the probability that the qubit will "flip" from the north and south, along the z-axis pole when matching ω to the Larmor frequency is greatest when the qubit starts at the state of |1> or |0>. The simulator will assume that the starting state of the qubit is its current state when the "Start" button is hit. If the Rabi Field simulation is stopped and started multiple times, each time it is started, the simulator will assume that the original state of the qubit is the last place that the Rabi Field stopped it. This means that the Rabi field cannot be paused. Since the starting state affects the overall path of the qubit, the qubit must be put at the original state to replay the same evolution.