The record/playback functionality allows users to record a sequence of operators that act upon the qubit states. The recording function allows the user to use the custom operator to create operators and have them act on the qubits. As they are applied to the qubits, they are recorded in the order that they are applied. The recorded operators can then be saved to a file for playback later. The playback functionality allows the user to load a saved file and then "play" or have the operators applied to the qubit state in the same order that they were recorded. The speed at which the operators are applied can be varied and the user can choose to individually step through each operator.
When the user clicks on the "Record/Playback" tab, the first screen that comes up allows the user to decide to record a series of operators, or play them back. This is seen in figure below.
When the user clicks on the record screen, the qubit state panel is replaced with the record panel and the only tab that is available on the bottom left is the "Custom Operator" tab. At this point, the simulator is in recording mode and any operator that is applied to the qubits will be recorded on the top left record panel. The figure below shows the default state with the recording panel on the top and the custom operator panel on the bottom.
As the operators are applied to the qubits, the record panel will show the value of the operator. The operator at the top of the list is the first operator that is applied. Each operator applied after that will appear below in the order that they are applied to the qubits. The Custom operator tab at the bottom works in the same manner when applying an operator to a qubit state. When all the desired operators have been recorded, the user can save the recorded operators by clicking on the "Save" button in the record panel. This will bring up a file explorer dialog to choose the file name and location.
The second part of functionality described is the playback function. When the user clicks on "Playback", they will have to select a file to playback. Currently, the user must select a file that has the extension ".bso". This stands for Bloch Sphere operators. When a file has been selected, the playback tab will be displayed in the bottom right. The figure below shows the state of the playback after a file has been loaded.
After the recorded operators have been loaded, there are several things that can be done to play back the operators. The first is the delay. The user can set the delay between the acting on the qubits. The standard delay is half a second. That means that the application will wait one half of a second between applying the current operator and the next operator. The delay can be changed as long as the application is not playing back the operators. To start the playback, the user should click the "Play" button. This will apply the first operator and then wait the delay before applying the next operator and continuing on. At any time, the user can pause the playback by hitting the "Pause" button. The pause button is only enabled though when the operators are being played back. Additionally, if the playback is paused, then the user can manually step through each of the operators by hitting the "Step" button. This will apply the next operator in the playback sequence. The operator application sequence can be set back to the first operator by hitting the "Restart" button. When playback is finished, the user should click the "End Playback" to return to the normal simulator functionality. The record playback function allows users to view visually the evolution of the qubits as quantum operators are acted on them. The record and playback functionality gives the user the flexibility to apply any number of operators without restriction on the operators themselves. The simple format of the saved file also allows the user to translate the output of other applications to the Bloch sphere simulator to view that effect.