Ion chain motional mode measurement by fast scan with maximum weight matching method

An ion trap quantum computing system, comprising:

• a classical computer;
• a quantum processor comprising a plurality of trapped ions in an ion chain, each trapped ion having two hyperfine states;
• a system controller configured to execute a control program to control one or more laser beams to perform operations on the quantum processor;
• and
• non-volatile memory having a number of instructions stored therein which, when executed by one or more processors, causes the ion trap quantum computing system to perform operations comprising:
• measuring, by the system controller, a coupling strength of each of the plurality of trapped ions in the ion chain and each of a plurality of motional modes of the ion chain, wherein the plurality of trapped ions comprises a plurality of first trapped ions that are addressable by the one or more laser beams, and a plurality of second trapped ions that are not addressable by the one or more laser beams;
• computing, by the classical computer, a first map of the plurality of first trapped ions to the plurality of motional modes, wherein the plurality of motional mode comprises a plurality of first motional modes that are allocated by the first map and a plurality of second motional modes that are unallocated by the first map;
• measuring, by the system controller, frequencies of the plurality of first motional modes, by measuring motional sideband transitions in the plurality of first trapped ions;
• computing, by the classical computer, a second map of the plurality of first trapped ions to the plurality of second motional modes;
• measuring, by the system controller, frequencies of the plurality of second motional modes, by measuring motional sideband transitions in the first trapped ions that are mapped to the plurality of second motional modes;
• and
• outputting, by the classical computer, the measured frequencies of the plurality of motional modes, to be used for computing a pulse to be applied to the ion chain for performing an entangling gate operation between a pair of trapped ions in the ion chain.

A quantum computing system, comprising:

• a plurality of trapped ions in an ion chain, each of the trapped ions having two hyperfine states defining a qubit;
• one or more lasers configured to emit a laser beam, which is provided to the ion chain;
• a system controller configured to control the one or more lasers to perform first operations on the ion chain;
• and
• a classical computer configured to perform second operations, wherein
• the first operations comprise:
• measuring a coupling strength of each of a plurality of trapped ions in an ion chain and each of a plurality of motional modes of the ion chain, wherein the plurality of trapped ions comprises a plurality of first trapped ions that are addressable by laser beams, and a plurality of second trapped ions that are not addressable by laser beams,
• the second operations comprise:
• computing a first map of the plurality of first trapped ions to the plurality of motional modes, wherein the plurality of motional mode comprises a plurality of first motional modes that are allocated by the first map and a plurality of second motional modes that are unallocated by the first map,
• the first operations further comprise:
• measuring frequencies of the plurality of first motional modes, by measuring motional sideband transitions in the plurality of first trapped ions,
• the second operations further comprise:
• computing a second map of the plurality of first trapped ions to the plurality of second motional modes,
• the first operations further comprise:
• measuring frequencies of the plurality of second motional modes, by measuring motional sideband transitions in the first trapped ions that are mapped to the plurality of second motional modes, and
• the second operations further comprise:
• outputting, by the classical computer, the measured frequencies of the plurality of motional modes, to be used for computing a pulse to be applied to the ion chain for performing an entangling gate operation between a pair of trapped ions in the ion chain.