Local Motional Mode Cooling for Long Ion Chains

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Solution Overview

Problem

As the size of a trapped ion processor increases, the process of sideband cooling collective motional modes becomes longer, leading to incomplete cooling and reheating due to competing heating rates, making it challenging to achieve the motional ground state in a timely manner.

Innovation Solution

The method involves driving sideband transitions faster for local motional modes than collective motional modes, allowing for parallel cooling of all ions in the chain, which reduces the overall cooling duration by exciting and de-exciting local motional modes associated with individual ions until they reach a ground state.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If sideband cooling is applied to collective motional modes in a long ion chain, then cooling of all collective modes is achieved, but the cooling process becomes excessively long and incomplete cooling occurs due to competing heating rates

Engineering Contradiction:

Improvemotional temperature of collective modesVSAvoidcooling duration

Core Design Contradiction:

TemperatureVSLoss of time

Solution Approach 1:

The patent segments the cooling process by distinguishing between two types of motional modes: collective modes (involving motion of multiple ions together) and local modes (involving motion of individual ions). By segmenting the cooling approach, the patent applies different cooling strategies to different mode types, using faster local mode cooling followed by collective mode cooling, thereby reducing the total cooling time while achieving complete cooling of all modes.

Inventive Principle:

Principle #1Segmentation

2Quantity of substance

If the number of qubits or ions in the chain is increased to expand processor size, then processing capacity is improved, but the sideband cooling process takes longer and prevents achieving the motional ground state

Engineering Contradiction:

Improvenumber of ions in the chainVSAvoidachievement of motional ground state

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies preliminary action by first cooling the local modes of individual ions before proceeding to cool the collective modes of the entire chain. This preliminary cooling of local modes reduces the initial thermal population, enabling the subsequent collective mode cooling to reach the motional ground state even in longer chains with more ions, thereby maintaining reliability as processor size increases.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If slow sideband driving is used to individually address each collective motional mode, then mode selectivity is maintained, but the overall cooling process becomes excessively long

Engineering Contradiction:

Improvemode addressing selectivityVSAvoidcooling rate

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent segments the cooling process into two distinct phases: first cooling local modes individually (which can be done faster), then cooling collective modes with proper selectivity. This segmentation allows the system to achieve both high productivity in the first phase and mode selectivity in the second phase, resolving the contradiction between cooling rate and selectivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent maintains continuity of useful action by seamlessly transitioning from local mode cooling to collective mode cooling without interruption. The local mode cooling continuously reduces thermal population throughout the chain, and this continuous cooling action is then followed by continuous collective mode cooling, ensuring that the entire process remains productive while maintaining selectivity where needed.

Inventive Principle:

Principle #20Continuity of useful action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach efficiently cools the collective motional modes of a long ion chain to near the ground state, improving the fidelity of gate operations in ion trap processors by reducing the cooling time and avoiding reheating, while maintaining the same number of cooling cycles as collective mode cooling.

Implementation Method 1

sideband transitions that are part of the cooling down sequence are driven faster for the local motional modes than for collective motional modes

Methodology Applied

Scientific EffectSideband transitions:

Implementation Method 2

phonons are removed from the ions in the chain of ions by exciting and de-exciting local motional modes

Methodology Applied

Scientific EffectPhonon removal:

Data Source

PatentUS11954560B2Fast cooling of ion motion in a long chain using local modes

Publication Date: 2024.04.09 IONQ INC

AI summary

Aspects of the present disclosure describe techniques for fast cooling of ion motion in a long chain using local motional modes. For example, a method is described for cooling down ions in a chain of ions that includes performing a cooling down sequence in which phonons are removed from the ions in the chain of ions by exciting and de-exciting local motional modes associated with individual ions, wherein sideband transitions that are part of the cooling down sequence are driven faster for the local motional modes than for collective motional modes for the same chain of ions; and completing the cooling down sequence when the local motional modes reach a ground state. A corresponding system and computer-readable storage medium for fast cooling of ion motion in a long chain using local motional modes are also described.