EP-4742109-A1 - FAST AND HIGH-FIDELITY QUANTUM GATES USING DIPOLE-DIPOLE INTERACTIONS

EP4742109A1EP 4742109 A1EP4742109 A1EP 4742109A1EP-4742109-A1

Abstract

The present disclosure relates to an apparatus for performing a quantum gate on a pair of atomic particles in a quantum register, comprising: a laser source, a microwave source, a set of optical elements configured to direct laser radiation generated by the laser source onto the pair of atomic particles, a microwave antenna, coupled to the microwave source, and configured to illuminate the pair of atomic particles with microwave radiation generated by the microwave source, wherein the microwave source is configured to control a duration, an intensity, a detuning and / or a phase of the microwave radiation, a laser modulator configured to control a duration, an intensity, a detuning and / or a phase of the laser radiation directed to the pair of atomic particles, and a control unit configured to control the laser modulator and the microwave source to illuminate the pair of atomic particles with modulated laser radiation and modulated microwave radiation to perform the quantum gate on the pair of atomic particles.

Inventors

GIUDICI, GIULIANO
VERONI, Stefano
GIUDICE, Giacomo
PICHLER, Hannes
ZEIHER, Johannes

Assignees

PlanQC GmbH

Dates

Publication Date: 20260513
Application Date: 20241111

Claims (15)

Method (300) for performing a quantum gate on a pair of atomic particles (100) serving as qubits for quantum computing, comprising: illuminating (310) the pair of atomic particles with a first electromagnetic radiation such that in each atomic particle a first qubit state 11) is coupled to a first Rydberg state |r 1 〉; and illuminating (320) the pair of atomic particles with a second electromagnetic radiation such that in each atomic particle the first Rydberg state |r 1 〉 is coupled to a second Rydberg state |r 2 〉, such that a dipole-dipole interaction is induced between the pair of atomic particles.
Method of claim 1, wherein the first electromagnetic radiation comprises laser radiation and the second electromagnetic radiation comprises microwave radiation.
Method of claim 1, wherein illuminating the pair of atomic particles with the first and the second electromagnetic radiation comprises: applying the first and the second electromagnetic radiation to the pair of atomic particles in form of at least two radiation pulses.
Method of claim 3, wherein the at least two radiation pulses are applied to the pair of atomic particles at least partially simultaneously.
Method of claims 1 to 4, wherein illuminating the pair of atomic particles with the first and the second electromagnetic radiation comprises: determining a pulse duration for the first and the second electromagnetic radiation and one or more time-dependent pulse parameters, including one or more of a pulse amplitude, a pulse phase, a detuning; and modulating the first and the second electromagnetic radiation based on the determined one or more time-dependent pulse parameters during the pulse duration, such that the dipole-dipole interaction between the two atomic particles realizes the quantum gate for the pair of atomic particles.
Method of claim 5, wherein determining the time-dependent pulse parameters comprises: determining the time-dependent pulse parameters based on optimizing a fidelity of the quantum gate; and / or determining the time-dependent pulse parameters based on optimizing a robustness of the quantum gate against inter-particle distance fluctuations of the pair of atomic particles.
Method of claim 6, wherein optimizing the robustness of the quantum gate against the inter-particle distance fluctuations of the pair of atomic particles further comprises: optimizing the fidelity of the quantum gate in presence of fluctuations of a dipolar interaction strength and / or a van der Waals interaction strength for the pair of atomic particles induced by the inter-particle distance fluctuations of the pair of atomic particles.
Method of any of claims 5 to 7, wherein determining the time-dependent pulse parameters further comprises: determining the time-dependent pulse parameters based on performing an iterative numerical optimization method, preferably a gradient ascent pulse engineering, GRAPE, optimization method.
Method of any of claims 1 to 8, wherein the quantum gate is a two-qubit entangling gate; and / or wherein the pair of atomic particles are part of a neutral atom quantum register formed by an array of optical traps for atomic particles inside a vacuum chamber.
Apparatus for performing a quantum gate on a pair of atomic particles (100) in a quantum register (512), comprising: a laser source (705); a microwave source (710); a set of optical elements (715) configured to direct laser radiation generated by the laser source onto the pair of atomic particles; a microwave antenna (720), coupled to the microwave source, and configured to illuminate the pair of atomic particles with microwave radiation generated by the microwave source, wherein the microwave source is configured to control a duration, an intensity, a detuning and / or a phase of the microwave radiation; a laser modulator (725) configured to control a duration, an intensity, a detuning and / or a phase of the laser radiation directed to the pair of atomic particles; a control unit (730) configured to control the laser modulator and the microwave source to illuminate the pair of atomic particles with modulated laser radiation and modulated microwave radiation to perform the quantum gate on the pair of atomic particles.
Apparatus of claim 10, wherein the control unit is further configured to control the laser modulator and the microwave source to perform the quantum gate by carrying out the steps to the method of any of claims 1 to 9.
Method (400) for quantum computing, comprising: trapping (420) a plurality of atomic particles in an array of optical traps forming a quantum register of trapped particle qubits inside a vacuum chamber; performing (430) a set of quantum gate operations of a quantum computing algorithm on a selected subset of the trapped particle qubits based on dipole-dipole interactions by performing the steps of the method of any of the claims 1 to 9; and determining (440) a result of the quantum computing algorithm by measuring a state of at least the selected subset of trapped particle qubits.
Method for quantum computing of claim 12, further comprising: obtaining (410) a set of instructions for performing the set of quantum gate operations of the quantum computing algorithm on the selected subset of the trapped particle qubits of the quantum register; and outputting (450) data corresponding to the result of the quantum computing algorithm.
Method for quantum computing of claim 13, wherein obtaining the set of instructions for performing the set of quantum gate operations of the quantum computing algorithm comprises obtaining the set of instructions from a remote user device via a network; and / or wherein outputting the data corresponding to the result of the quantum computing algorithm comprises sending, to the remote user device via the network, the data corresponding to the result of the quantum computing algorithm.
Neutral atom quantum computer (500) configured to operate a neutral atom quantum register (512) inside a vacuum chamber (510) to perform a quantum computing algorithm and comprising means to carry out the steps of the method of any of claims 12 to 14.

Description

FIELD OF INVENTION The present disclosure relates to methods and devices for performing fast, high-fidelity, and robust quantum gates on atomic particles, such as neutral atoms, using radiation induced dipole-dipole interactions between pairs of atomic particles. INTRODUCTION The ability to perform high-fidelity quantum gates in a fast and robust manner is a key requirement for building useful quantum computing devices. As known in the art, the computational advantage provided by quantum computing devices as compared to classical computers may be limited by the fidelity, speed and/ or robustness of individual quantum gates. A sequence of an arbitrary number of such gates may implement a quantum algorithm. Such quantum gates generally act on a plurality of qubits of a quantum register. Such quantum registers may be realized, for instance, by trapping, inside a vacuum chamber, neutral atoms (such as rubidium, cesium, strontium or ytterbium atoms, etc.) or other types of atomic particles (molecules, ions, etc.) in arrays of optical tweezer traps or optical lattices or combinations thereof. Typically, realizing quantum gates for a group of two or more qubits requires interactions between qubits. For example, such interactions may be engineered using Rydberg states of neutral atoms (see e.g.: L. Henrit et al: Quantum computing with neutral atoms, Quantum 4, 327 (2020)). Neutral atom quantum registers provide long coherence times, scalability and reconfigurable geometries for realizing arbitrary interaction connectivity between the qubits of the quantum register. For example, two-qubit quantum gates involving Rydberg states and van der Waals interactions have been experimentally realized using rubidium atoms (see S. J. Evered et al., High-fidelity parallel entangling gates on a neutral-atom quantum computer, Nature 622, pp. 268-272), achieving up to 99.5% gate fidelity. There remains a perpetual need for improving fidelity, speed and / or the robustness of two-qubit quantum gates for atomic particles. SUMMARY Realizing two-qubit gates for a pair of atomic particles typically includes coupling internal states of the atomic particles to a Rydberg level via electromagnetic radiation (such as laser radiation) such that the pair of atomic particles can interact with each other through van der Waals forces. The length scale or effective range of this interaction is typically on the same order as the physical distance between the pair of atomic particles in a typical quantum register e.g., formed by trapping the atomic particles in an optical lattice or an optical tweezer trap array. Parameters of such electromagnetic radiation (e.g., duration, amplitude, frequency, phase, etc.), may be modulated in time in such a way that the desired two-qubit gate operation is realized. The modulation required to achieve the desired two-qubit gate is not unique, providing a degree of freedom that can be exploited to minimize execution time of the quantum gate and / or to maximize fidelity and / or the robustness of the quantum gate against, for instance, experimental imperfections, such as fluctuations of the intensity of the electromagnetic radiation. Fast execution times can be particularly relevant as the finite lifetime of the Rydberg state involved in the scheme above is considered a major source of decoherence that may lead to undesirable errors in the quantum computation. The fidelity of quantum gates may be limited, inter alia, by the finite lifetime of the Rydberg states involved in mediating the van der Waals interactions between the atomic particles. Thus, reducing the execution time of a quantum gate can benefit its fidelity. Minimizing the quantum gate execution time may be facilitated by a large interacting strength. Further, the fidelity of the quantum gate may also depend on how robust execution of the quantum gate is to small variations in gate execution parameters, including but not limited to the amplitude and the phase of the electromagnetic radiation as well as the distance between the two atomic particles. Such variations may be caused by the unstable environmentally conditions, such that mitigating and / or compensating them during gate execution may be preferred over determining and eliminating their sources. Thus, reducing the sensitivity of the quantum gate fidelity to the gate execution parameters may benefit the experimental fidelity of the quantum gate. To improve speed, fidelity and / or robustness of multi qubit gates the present disclosure provides, inter alia, a method for performing a quantum gate on a pair of atomic particles according to claim 1, an apparatus for performing a quantum gate on a pair of atomic particles in a quantum register according to claim 10, a related method for quantum computing according to claim 12, and a neutral atom quantum computer according to claim 15. The corresponding dependent claims relate to further aspects of exemplary and / or advantageous implementations. In some