Patent Description:
Aspects of the present disclosure relate generally to the cooling of ions in a chain, and more specifically, to the fast cooling of ion motion in a long chain using local modes. Relevant prior art is described in <NPL>.

The cooling of all of the collective motional modes of a trapped ion chain, such as the one used in a trapped ion quantum computer or a quantum information processing (QIP) system, is necessary for reliable high fidelity qubit operations. The cooling process is usually implemented by coherently driving motional sideband transitions to remove motional excitations or phonons from each of these collective motional modes. This requires driving sideband transitions at a rate slow enough such that each collective motional mode can be individually addressed without exciting neighboring collective motional modes while cooling them at the same time. As the size of a trapped ion processor is increased, that is, as the number of qubits or ions in the chain increases, the process of sideband cooling of the collective motional modes takes longer to achieve the cooling of all of the collective motional modes of the chain. This can prevent achieving the motional ground state of each of the collective motional modes because of a competing rate of heating of the trapped ions, leading to undesired reheating of the modes as a result of a lengthy sideband cooling processes.

It is therefore desirable to devise alternate methods of cooling the collective motion of a trapped ion chain that reduces the overall duration of this process.

Observation of Hopping and Blockade of Bosons in a Trapped Ion Spin Chain (<NPL> describes a method of preparing single excitations at individual sites of a Coulomb crystal of trapped ions with coupled bosons.

In an aspect of this disclosure, a method for cooling down ions in a chain of ions is described 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, where 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. The method further includes completing the cooling down sequence when the local motional modes reach a ground state.

In another aspect of this disclosure, a system for cooling down ions in a chain of ions is described that includes an optical controller configured to perform 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, where 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. The optical controller is further configured to complete the cooling down sequence when the local motional modes reach a ground state.

In yet another aspect of this disclosure, a computer-readable storage medium configured to store code executable by a processor is described that includes code for 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. The computer-readable storage medium further includes code for completing the cooling down sequence when the local motional modes reach a ground state.

As described above, by increasing the size of a trapped ion processor to increase computing capacity, the number of qubits or ions in the chain of ions used as the processor increases and the process of sideband cooling of the collective motional modes takes longer to achieve the cooling of all of the collective motional modes of the chain. This can prevent achieving the motional ground state of each of the collective motional modes because of a competing rate of heating of the trapped ions, leading to undesired reheating of the modes as a result of a lengthy sideband cooling processes. It is therefore desirable to devise alternate methods of cooling the collective motion of a trapped ion chain that reduces the overall duration of this process. One such method requires driving of the local motional mode sideband of each ion and using all ions in a chain in parallel during the cooling process.

Accordingly, the present disclosure describes the use of local modes of motion of individual ions in a chain for the cooling of the collective motional modes of the chain. Local modes can be excited if the motion of any ion in the chain is perturbed faster than the speed at which the excitation travels or hops to neighboring ions due to the strong electrostatic repulsion between the ion. By coherently driving the motional sideband transitions of the local motional modes corresponding to each ion of the chain, it may be possible to cool all local motional modes in parallel by driving all ions in the chain simultaneously. This approach leads to the cooling of the collective motional modes of the chain to near the ground state, which then improves the fidelity of gate operations in the ion trap processor. The overall cooling process using local motional modes is shorter compared to the cooling process using collective motional modes because of the use of multiple ions in the chain simultaneously during cooling, because the driving of sideband transitions resonant with the local motional modes are performed much faster than driving of sideband transitions resonant with the collective motional modes, and because the number of cooling cycles required is comparable or the same as that required in the collective motional mode cooling, which is governed by the initial temperature (average number of phonon excitations) of the ion chain.

Thus, the present disclosure describes a mechanism or scheme for more efficiently cooling long ion chains by using local modes of motion. Local modes of motion is not a concept or approach that is currently widely used in connection with ion traps, and typically only appears in the context of larger ion chains. For example, when there is a long chain of ions, a perturbation of the motion of single or individual ions in the chain (instead of collective motions of multiple or all ions in the chain) may take some time to propagate throughout the chain because the chain is very long. Until the motion begins to propagate it is merely a local motion of an ion. The chain of ions can be viewed as multiple masses (e.g., ions) that are connected by springs. When the ions in the chain oscillate together it is referred to as a collective motion and the various modes of oscillation as collective motional modes, collective modes of motion, or normal modes of motion. There may be collective motional modes when the entire chain oscillates at the same frequency. Moreover, there are as many collective motional modes as there are ions in the chain (e.g., there is a one-to-one correspondence between the number of collective motional modes and ions in the chain). During collective motional modes, the ions in the entire chain are in communication with each other as the whole chain moves together when viewed from a long time scale. In a short time scale, however, the motion of one ion affects the motion of another ion and if this is averaged over time it looks like a collective motional mode.

Collective motional modes can be used to implement quantum gates, such as two-qubit quantum gates, for example. In long chains of ions, collective motional modes form the medium of information exchange among the ions. For example, a two-qubit quantum gate can be implemented by entangling the qubits (e.g., the ions) with different ions in the chain using these normal or collective motional modes.

In order to achieve high fidelity in the quantum operations, it is necessary to cool down the collective motional modes by removing excitations from them. This may be done by cooling down the ions in the chain to a ground state (e.g., freeze the ions), and do so for each of the collective motional modes. One approach is to excite a particular collective motional mode, which has a particular resonant frequency, and while being resonant at that frequency, drive a sideband transition to remove the motional excitation by applying a laser beam on the ions to perform a Raman transition. Based on this approach, it is possible to remove unit packet, quanta, or phonons from the collective motional modes in order to cool them down.

This cooling down process can become very time and resource intensive. As the chains become longer there are many more collective motional modes to cool down because the number of motional modes increases linearly with the number of ions in the chain.

Another issue that arises is that even when the chain length increases (i.e., the number of ions is increased), the spacing between the ions in the ion chain (i.e., in the trap holding the ions) does not change. This is because the spacing between ions is dictated by limitations in the optics used in the system and/or by the way in which light is collected from the ions. That is, the various optical set ups that enable control and manipulation of the ions in the chain are typically optimized for a certain spacing between the ions (e.g., typically in a range of <NUM> - <NUM> microns). Therefore, the spacing between the ions in the chain is system-dependent and typically remains the same.

<FIG> shows a diagram <NUM> that illustrates multiple atomic ions <NUM> trapped in a linear or one-dimensional arrangement, e.g., a linear crystal or chain of ions <NUM>, and having a same spacing <NUM> between atomic ions <NUM>. As used in this disclosure, the terms "atomic ions" and "ions" may be used interchangeably. The ions <NUM> may be trapped and configured into the chain <NUM> by using a linear radio frequency (RF) trap such as a linear RF Paul trap (the chain <NUM> can be inside a vacuum chamber not shown). In the example shown in <FIG>, the trap may include electrodes for trapping multiple Ytterbium ions (e.g., <NUM>Yb+ ions) which are confined in the chain <NUM> and are laser-cooled to be nearly at rest. Other atomic species may also be used. The number of atomic ions trapped can be configurable and more or fewer atomic ions may be trapped than those shown in <FIG>. In an example, the number of ions that may be trapped is N, where N > <NUM> and where N is a number as large as <NUM> or even larger, with some implementations having N = <NUM>. The ions are illuminated with laser (optical) radiation tuned to a resonance in <NUM>Yb+ and the fluorescence of the ions may be imaged onto a camera. In this example, ions may be separated by about <NUM> microns (µm) from each other as may be shown by fluorescence. The separation of the atomic ions is a function of a balance between the external confinement force and Coulomb repulsion, and is conditioned, as described above, on the optimization of the optical set ups that enable control and manipulation of the ions in the chain <NUM>.

By increasing the number of ions in the chain <NUM> so that a quantum processor (e.g., a processor based on qubits made from the ions in the chain <NUM>) can have more qubits, the number of collective motional modes associated with the chain <NUM> also increases. Since the size of the chain <NUM> does not change significantly even as more ions are added given the small spacing between ions, the frequencies associated with an increasing number of collective motional modes start to get closer together. This may be referred to as spectral crowding. In such a case, while it is desirable to drive each collective motional mode separately during the cooling process, it may become difficult to preferentially drive one collective motional mode without driving another collective motional mode as their frequencies get close together. To avoid exciting another collective motional mode, the collective motional mode under consideration needs to be driven very slowly. Therefore, the cooling down of collective motional modes is fundamentally limited by the time scales that are needed to properly drive the collective motional modes. As a result, when trying to perform the cooling down of the collective motional modes by removing phonons using a sideband transition, the overall time it takes for a sequence needed to cool down the collective motional modes can become really long, affecting the ability of having a quantum computing system quickly available and ready to perform a quantum operation.

<FIG> illustrate diagrams 200a-200c, which show examples of different collective mode frequencies for trapped ion chains in accordance with aspects of the disclosure. Each of the diagrams shows various collective motional modes for trapped ion chains having different number of ions within a frequency band. The diagram 200a in <FIG> corresponds to an ion chain having <NUM> ions and therefore <NUM> frequencies are shown for the collective motional modes. The diagram 200b in <FIG> corresponds to an ion chain having <NUM> ions and therefore <NUM> frequencies are shown for the collective motional modes. Similarly, the diagram 200c in <FIG> corresponds to an ion chain having <NUM> ions and therefore <NUM> frequencies are shown for the collective motional modes. In this example, the transverse confinement and the average spacing between adjacent ions in the chain are kept constant for all cases at <NUM> and <NUM> microns, respectively. These calculations show that as the chain length is increased in a trapped-ion processor, spectral crowding of collective motional modes occurs where the spacing between adjacent mode frequencies, shown as δω, decreases in value. The value of δω may therefore refer to a frequency splitting between any two collective or normal motional modes. Thus, δω dictates how slowly to drive the sidebands of the collective motional modes to cool down the modes. As δω goes down, the cooling duration goes up as <NUM>/ δω.

<FIG> illustrates a diagram <NUM> an example a sideband cooling sequence as described above, where the sideband cooling sequence consists of repetitive cycles of sideband pi-pulses and optical pumping of the qubit. For example, a first cycle 310a is shown to have a sideband pi-pulse 315a followed by an optical pumping 320a. A second cycle 310b is shown to have a sideband pi-pulse 315b followed by an optical pumping 320b. Similar cycles are then repeated. The sideband pi-pulses (e.g., 315a, 315b) are used to remove a phonon but they also change the spin state of the qubit. The optical pumping (e.g., 320a, 320b) are then used to bring the spin state back to its original form. The sideband pi-pulses are of duration tπ, which is set by the choice of sideband cooling scheme used. A collective motional mode sideband cooling scheme requires tπ > <NUM>/δω, such that each mode is individually resolved and addressed. The number of cycles required for cooling the motion of the ion chain to near ground state is proportional to the average vibrational/phonon excitation in each collective motional mode. Because of spectral crowding as shown in <FIG>, the collective motional mode sideband cooling gets slower with increasing chain length (i.e., the number of ions in the chain). In other words, as the frequencies become more crowded and δω becomes smaller when the number of ions in the chain increases, the duration of the sideband pi-pulses (e.g., 315a, 315b) gets longer.

To reduce the time it takes to cool down the motion of the ion chain to near ground state, and to avoid making such process significantly longer as the number of ions increases, the present disclosure proposes the use of local motional modes or local modes of motion instead of the collective motional modes. There are some advantages to this approach. Because the process involves the removal of phonons, cooling down the local motional modes achieves the same result as cooling down the collective motional modes by cooling down the ion and removing motional excitations. That is, since there is a relationship (e.g., a linear transformation) between collective and local motional modes, the removal of phonons has the same effect in both contexts.

To remove phonons using the local motional modes and sideband transitions, and to ensure that the phonons are being removed from the local motional modes, it is important to drive that transition really fast. So this approach by default increases the operational speed of the cooling down process. The reason to drive the transitions fast is because the concept of the local motional mode is only valid in the context of really short time scales. Therefore, local motional modes need to be driven faster than they can hop or jump from one ion to a neighboring ion. Generally, if an ion is made to move in its position it tends to perturb neighboring ions. However, if the ion is made to move fast enough, faster than information can travel from the ion to neighboring ions, then it is possible to excite or de-excite the ion without affecting the neighboring ions. This approach allows for the local motional modes are used and speeds up the cooling down process.

<FIG> shows a diagram <NUM> illustrating an example of a local motional mode of a single ion <NUM> in an ion chain. The diagram <NUM> shows few ions inside a longer ion chain where the local motional mode of a single ion <NUM> (e.g., ion i) is excited or de-excited using a laser beam <NUM> that changes its local transverse motional excitation or phonon number. This local transverse motion is in the direction shown by solid black arrows (e.g., up-down arrows about the ion <NUM>). Due to electrostatic repulsion of this ion with neighboring ions, this local mode excitation may hop or jump from the ion <NUM> (e.g., the ion i) to its neighboring ions j at a rate Hij. The rate of hopping is determined by the uniform spacing between ions D (e.g., spacing <NUM> in the diagram <NUM> in <FIG>).

<FIG> shows a diagram <NUM> illustrating an example of a hopping rate between ions in a trapped ion chain. This particular example shows the rate of hopping between ions in a chain of trapped Ytterbium ions with uniform transverse confinement of about <NUM> with a variable but uniformly (or nearly uniformly) set spacing between the ions of a chain. The line 510a correspond to the hopping rate when the ion spacing (e.g., D) is <NUM> microns, while lines 510b and 510c correspond to the hopping rate when the ion spacing is <NUM> microns and <NUM> microns, respectively. The hopping rate is dependent on the ion spacing and not on the overall length of the chain. Moreover, the hopping rate is strongest between nearest neighboring ions and decreases quickly as a cube of the distance between ions. Therefore it is necessary to manipulate local motional modes (e.g., local phonon modes) of each ion during a local mode sideband cooling protocol as shown in the diagram <NUM> in <FIG> using tπ < <NUM>/Hi, i + <NUM>. This requires much faster sideband-pi pulses (e.g., sideband pi-pulses 315a, 315b) compared to those used in collective motional mode sideband cooling. Faster sideband-pi pulses may require more laser power (e.g., larger power for the laser beam <NUM> in the diagram <NUM> in <FIG>) to be used so that the modes are driven faster. However, the number of repetitions required is the same as it is still set by the initial temperature of the ion chain. Additionally, it is possible to use multiple laser beams, each tuned to de-excite individual ions of the chain simultaneously thereby cooling the local motional modes in parallel. The interspersed pump durations (e.g., pump 320a, 320b) allows the local motional mode de-excitations to propagate over the entire chain thereby cooling the collective motion of the chain. Therefore, the local motional mode sideband cooling technique dramatically reduces the overall duration for cooling of a long ion chain to its motional ground state.

The diagram <NUM> generally shows that the hopping rate falls very quickly with distance and it does not change substantially when changing the spacing between ions in the chain. Therefore, when manipulating local motional modes, the rate at which the local motional modes are driven is governed mainly by the spacing between the ions and not so much by the size of the chain. On the other hand, and as described above, the size of the chain (i.e., the number of ions or qubits in the chain) does depend on the frequency splitting between any two collective or normal motional modes, δω.

As described above, the cooling down process using local motional modes can be performed in parallel, that is, each of the ions in the chain can be individually and concurrently driven fast enough such that the local motion of the ion can be de-excited without information traveling from the ion to any neighboring ions. If the information were to travel to a neighboring ion before the one ion is de-excited, then control of the local motional mode may be lost.

Driving the local motional modes in parallel has at least two benefits. First, the local motional modes need to be driven fast and this makes by default the process faster, and second, it is possible to drive all local motional modes at the same time (e.g., simultaneously or concurrently), which also expedites processing.

In addition, it is not necessary to drive all of the ions to cool the local motional modes. It is possible to drive just a few ions in the chain for which there is an experimental level of comfort. For example, the chain of ions may have some ions that are considered operational ions, that is, ions used as qubits for various operations, computations, or experiments. There may be one or more ions in the chain referred to as spectator ions, which are used to help stabilize the chain but for which Raman transitions are not performed.

Whether all of the ions in the chain are driven or just a subset of the ions in the chain are driven it is possible to cool down the entire chain because after removing phonon excitations from the local motional modes, the information travels fast across the chain. That is, after removing energy from one ion (e.g., by removing one or more phonons) it is essentially removed from the whole set of ions in the chain because energy will flow back into that ion from the rest of ions in the chain. Unlike collective or normal motional modes, which are stable eigen modes of oscillation and are independent from each other, local motional modes tend to interact with each other. For example, and as described above, if a phonon is removed from one local motional mode another local motional mode may lose a phonon that may hop over to fill out the phonon that was removed. Therefore, it is possible to cool down the entire chain because local modes interact with each other. This can be done by performing a number of cooling cycles to remove all of the phonons of the local motional modes in the system and bring those modes to the ground state, which also implies that the collective or normal motional modes in the system are in the ground state. It is therefore possible to achieve collective motional modes in the ground state by cooling down the local motional modes really fast.

<FIG> is a block diagram illustrating an example of a quantum information processing (QIP) system <NUM> in accordance with aspects of this disclosure. The QIP system <NUM> may also be referred to as a quantum computing system, a computer device, a trapped ion system, a trapped ion quantum computer, or the like. In an aspect, the QIP system <NUM> may be configured to perform quantum computations and quantum experiments. Moreover, the QIP system <NUM> may be configured to perform cooling of ions in a chain of ions to prepare the chain to be used as a processor or part of a processor. More specifically, the QIP system <NUM> may be configured to perform fast cooling of ion motion in a chain using local motional modes. Alternatively, the QIP system <NUM> may be configured to perform cooling of ion motion in a chain using collective or normal motional modes. The length of the chain of ions may vary, that is, the number of ions (e.g., qubits) in the chain can be dynamically be increased or decreased.

The QIP system <NUM> can include a source <NUM> that provides atomic species (e.g., a flux of neutral atoms) to a chamber <NUM> having an ion trap <NUM> that traps the atomic species once ionized (e.g., photoionized) by an optical controller <NUM>. The ion trap <NUM> may be used to trap ions into a linear array such as the chain <NUM> described above in connection with the diagram <NUM> in <FIG>. The ion trap <NUM> may be considered to be a trapped ion processor or part of one. Optical sources <NUM> in the optical controller <NUM> may include one or more laser sources (e.g., sources of optical or laser beams) that can be used for ionization of the atomic species, control of the atomic ions, for fluorescence of the atomic ions that can be monitored and tracked by image processing algorithms operating in an imaging system <NUM> in the optical controller <NUM>, and/or to perform the cool down functions described in this disclosure. The optical sources <NUM> may be configured to control and generate a linear array of laser beams to perform parallel operations on the ions of the chain in the ion trap <NUM>. In an aspect, the optical sources <NUM> may be implemented separately from the optical controller <NUM>.

The imaging system <NUM> can include a high resolution imager (e.g., CCD camera) for monitoring the atoms while they are being provided to the ion trap <NUM> and/or the atoms after they have been provided to the ion trap <NUM> and photoionized. In an aspect, the imaging system <NUM> can be implemented separate from the optical controller <NUM>, however, the use of fluorescence to detect, identify, label, and/or control atomic ions using image processing algorithms may need to be coordinated with the optical controller <NUM>.

The QIP system <NUM> may also include an algorithms component <NUM> that may operate with other parts of the QIP system <NUM> (not shown) to perform quantum algorithms or quantum operations, including a stack or sequence of combinations of single qubit operations and/or multi-qubit operations (e.g., two-qubit operations) as well as extended quantum computations. As such, the algorithms component <NUM> may provide instructions to various components of the QIP system <NUM> (e.g., to the optical controller <NUM>) to enable the implementation of the quantum algorithms or quantum operations.

The optical controller <NUM> may include a cool down component <NUM> that is configured to control various aspects of a cool down operation. For example, the cool down component <NUM> may control a sequence of cycles as described above in connection with the diagram <NUM> in <FIG>. In this regard, the cool down component <NUM> may control the duration of the sideband pi-pulses (e.g., the sideband pi-pulses 315a, 315b), the duration of the optical pumping (e.g., the pumps 320a, 320b), and/or the number and timing of sequence cycles (e.g., the cycles 310a, 310b).

The cool down component <NUM> may include a local modes 645a, which is a component configured to control and handle all aspects described herein for using local motional modes to cool down the ions in an ion chain. The cool down component <NUM> may optionally include a collective modes 645b, which is a component configured to control and handle all aspects described herein for using collective motional modes to cool down the ions in an ion chain. The cool down component <NUM> may be configured to select its operation to be based on the use of local motional modes (e.g., local modes 645a) or collective motional modes (e.g., collective modes 645b).

Referring now to <FIG>, illustrated is an example computer device <NUM> in accordance with aspects of the disclosure. The computer device <NUM> can represent a single computing device, multiple computing devices, or a distributed computing system, for example. The computer device <NUM> may be configured as a quantum computer (e.g., a QIP system), a classical computer, or a combination of quantum and classical computing functions. For example, the computer device <NUM> may be used to process information using quantum algorithms based on trapped ion technology and may therefore implement some of the techniques described in which local motional modes are used to cool down the ions in a chain of ions. A generic example of the computer device <NUM> as a QIP system that can implement the techniques described herein is illustrated in the example described above in connection with <FIG> and the QIP system <NUM>.

In one example, the computer device <NUM> may include a processor <NUM> (e.g., a trapped ion processor) for carrying out processing functions associated with one or more of the features described herein. For example, the processor <NUM> may be configured to control, coordinate, and/or perform aspects of manipulating quantum information stored in an ion or atom. The processor <NUM> may include a single or multiple set of processors or multi-core processors. Moreover, the processor <NUM> may be implemented as an integrated processing system and/or a distributed processing system. The processor <NUM> may include a central processing unit (CPU), a quantum processing unit (QPU), a graphics processing unit (GPU), or combination of those types of processors. In one aspect, the processor <NUM> may refer to a general processor of the computer device <NUM>, which may also include additional processors <NUM> to perform more specific functions. The processor <NUM> may involve using one or more trapped ions to perform quantum operations, algorithms, or simulations.

In an example, the computer device <NUM> may include a memory <NUM> for storing instructions executable by the processor <NUM> for carrying out the functions described herein. In an implementation, for example, the memory <NUM> may correspond to a computer-readable storage medium that stores code or instructions to perform one or more of the functions or operations described herein. In one example, the memory <NUM> may include instructions to perform aspects of a method <NUM> described below in connection with <FIG>. Just like the processor <NUM>, the memory <NUM> may refer to a general memory of the computer device <NUM>, which may also include additional memories <NUM> to store instructions and/or data for more specific functions.

Further, the computer device <NUM> may include a communications component <NUM> that provides for establishing and maintaining communications with one or more parties utilizing hardware, software, and services as described herein. The communications component <NUM> may carry communications between components on the computer device <NUM>, as well as between the computer device <NUM> and external devices, such as devices located across a communications network and/or devices serially or locally connected to computer device <NUM>. For example, the communications component <NUM> may include one or more buses, and may further include transmit chain components and receive chain components associated with a transmitter and receiver, respectively, operable for interfacing with external devices.

Additionally, the computer device <NUM> may include a data store <NUM>, which can be any suitable combination of hardware and/or software, that provides for mass storage of information, databases, and programs employed in connection with implementations described herein. For example, the data store <NUM> may be a data repository for operating system <NUM> (e.g., classical OS, or quantum OS). In one implementation, the data store <NUM> may include the memory <NUM>.

The computer device <NUM> may also include a user interface component <NUM> operable to receive inputs from a user of the computer device <NUM> and further operable to generate outputs for presentation to the user or to provide to a different system (directly or indirectly). The user interface component <NUM> may include one or more input devices, including but not limited to a keyboard, a number pad, a mouse, a touch-sensitive display, a digitizer, a navigation key, a function key, a microphone, a voice recognition component, any other mechanism capable of receiving an input from a user, or any combination thereof. Further, the user interface component <NUM> may include one or more output devices, including but not limited to a display, a speaker, a haptic feedback mechanism, a printer, any other mechanism capable of presenting an output to a user, or any combination thereof.

In an implementation, the user interface component <NUM> may transmit and/or receive messages corresponding to the operation of the operating system <NUM>. In addition, the processor <NUM> may execute the operating system <NUM> and/or applications or programs, and the memory <NUM> or the data store <NUM> may store them.

When the computer device <NUM> is implemented as part of a cloud-based infrastructure solution, the user interface component <NUM> may be used to allow a user of the cloud-based infrastructure solution to remotely interact with the computer device <NUM>.

<FIG> is a flow diagram that illustrates an example of a method <NUM> for cooling down ions in a chain of ions in accordance with aspects of this disclosure. In an aspect, the functions of the method <NUM> may be performed by one or more components of a trapped ion system or a QIP system such as the QIP system <NUM> and its components (e.g., optical controller <NUM> and its components or subcomponents). Similarly, the functions of the method <NUM> may be performed by one or more components of a computer device such as the computer device <NUM> and its components.

In <NUM>, the method <NUM> includes performing a cooling down sequence (see e.g., the diagram <NUM> in <FIG> as applied to local motional modes) 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, where 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. The ions in the chain of ions can be Ytterbium ions, although other types of ions can also be used.

In <NUM>, the method <NUM> includes completing the cooling down sequence when the local motional modes reach a ground state.

In another aspect of the method <NUM>, performing the cool down sequence includes generating a laser beam for exciting and de-exciting each of the local motional modes.

In another aspect of the method <NUM>, performing the cool down sequence includes exciting and de-exciting the local motional modes associated of multiple ions in parallel.

In another aspect of the method <NUM>, the ions in the chain of ions include operational ions and spectator ions, and performing the cool down sequence includes exciting and de-exciting the local motional modes associated with the operational ions.

In another aspect of the method <NUM>, the ions in the chain of ions are uniformly (or nearly or substantially uniformly) spaced and a spacing between the ions is in a range of <NUM> microns to <NUM> microns.

Claim 1:
A method (<NUM>) for cooling down a collective motion of ions in a chain of ions (<NUM>) in an ion trap, the method comprising:
performing a sideband cooling down sequence (<NUM>, <NUM>) by applying repetitive cycles of sideband pulses and optical pumping to individual ions in the chain of ions to excite and de-excite local motional modes of each of the individual ions to remove phonons therefrom, wherein a driving of sideband transitions during the sideband cooling down sequence is faster than a driving of sideband transitions resonant with collective motional modes for the same chain of ions in which the ions in the ion chain oscillate together, such that each ion is excited and de-excited without affecting a neighboring ion; and
completing the sideband cooling down sequence (<NUM>) when the local motional modes of each of the individual ions reach a ground state.