KR-20260068036-A - Apparatus and Method for Non-mediated Non-destructive Quantum State Detection of Ion Qubits via Motional Modes

KR20260068036AKR 20260068036 AKR20260068036 AKR 20260068036AKR-20260068036-A

Abstract

The present invention relates to an apparatus and method for non-destructively detecting the quantum state of an ion-based qubit. The apparatus of the present invention comprises an ion-based qubit portion levitating within an electromagnetic trap to maintain a quantum superposition or quantum entanglement state, a detection electrode on which an image charge corresponding to the charge distribution of the qubit is induced on its surface, a high-sensitivity sensor portion detecting a micro-electromagnetic interference signal according to the quantum state of the qubit, and a control portion analyzing the detected signal to determine the quantum state of the qubit. By reading the qubit quantum state using only electromagnetic inductive coupling without applying measurement photon energy to the ion-based qubit, wave function decay is minimized, and since the motion mode of the ion is not mediated, the motion mode is fully preserved in subsequent quantum gate operations. This achieves significant effects compared to laser fluorescence detection methods, such as coherence preservation, motion mode preservation, intermediate measurement capability, and laser-free integration.

Inventors

안범주

Assignees

안범주

Dates

Publication Date: 20260513
Application Date: 20260425

Claims (16)

In a device for non-destructively detecting the quantum state of an ion-based qubit, An ion-based qubit portion levitating and isolated within an electromagnetic trap so that at least one ion maintains a quantum superposition or quantum entanglement state; A detection electrode disposed adjacent to the above-mentioned ion-based qubit in a non-contact manner, wherein an image charge corresponding to the charge distribution of the qubit is induced on its surface; A high-sensitivity sensor unit that detects a micro-electromagnetic interference signal induced in the detection electrode by micro-vibrations or energy level changes according to the quantum state of the ion-based qubit; and It includes a control unit that analyzes the detected signal to determine the quantum state of the qubit, A non-destructive quantum state detection device characterized by reading information while minimizing the collapse of the quantum superposition state by utilizing only electromagnetic inductive coupling between the qubit and the detection electrode, without applying direct measurement photon energy to the ion-based qubit.
In paragraph 1, The |0> state and |1> state of the ion-based qubit have different electric multipole moments, and the multipole moment is at least one selected from the group consisting of static polarizability, electric quadrupole moment, and permanent electric dipole moment. A non-destructive quantum state detection device characterized in that the amount of change in the image charge induced in the detection electrode is determined by the difference in the multipole moment between the |0> state and the |1> state.
In paragraph 1, The resonant frequency of the resonant circuit included in the high-sensitivity sensor unit is positioned at least one octave apart from the secular frequency of the motional mode of the ion-based qubit, and Accordingly, the non-destructive quantum state detection device is characterized in that the micro electromagnetic interference signal induced in the detection electrode is directly induced by a change in multipole moment dependent on the internal quantum state of the qubit, without mediating a change in the motion amplitude of the ion-based qubit.
In paragraph 1, The detection electrode comprises a multipole matching detection electrode array composed of two or more partitioned regions spatially arranged to surround the ion-based qubit, and A non-destructive quantum state detection device characterized by further including a synchronous detection unit that differentially synthesizes image charge signals induced in each of the divided regions to cancel out the motion amplitude component of the ion-based qubit and extracts only the multipole moment component.
In paragraph 1, A non-destructive quantum state detection device characterized in that the operating condition of the high-sensitivity sensor unit is set to a dispersive regime in which the measurement-induced dephasing rate (Γ_φ,meas) is 1/10 or less of the intrinsic dephasing rate (Γ_φ,intrinsic) of the ion-based qubit, so as to be configured to preserve the quantum superposition state within a single measurement cycle.
In paragraph 1, A non-destructive quantum state detection device characterized in that the high-sensitivity sensor unit comprises at least one single charge resolution sensor selected from the group consisting of a single electron transistor (SET) and a superconducting quantum interference device (SQUID), and the charge sensitivity of the single charge resolution sensor is 10 μe/√Hz or less.
In paragraph 6, A non-destructive quantum state detection device, wherein the high-sensitivity sensor unit further comprises an impedance matching circuit including a superconducting toroidal inductor having an unloaded quality factor (Q) of 50,000 or more, disposed between the detection electrode and the single charge resolution sensor, and wherein the passband of the impedance matching circuit is matched within ±10% of the modulation frequency of the multipole moment signal of the ion-based qubit.
In paragraph 2, A non-destructive quantum state detection device characterized in that the ion-based qubit is a single atomic ion selected from the group consisting of 40 Ca + , 171 Yb + , 88 Sr + , Be9 + , 1³³Ba + , 201 Hg + , and 229 Th + , and the difference in multipole moment between the |0> state and the |1> state is derived from the electric quadrupole moment of the D5 /₂ level or F7 /₂ level of the single atomic ion.
In paragraph 4, A non-destructive quantum state detection device characterized in that each divided region of the multipole-matched detection electrode array is evenly divided and arranged in the azimuthal direction centered on the position of the ion-based qubit, and the gap between the divided regions is configured to be 1/5 or less of the distance between the ion-based qubit and the divided regions, thereby being spatially matched with a quadrupole or octupole multipole moment.
In Paragraph 9, A non-destructive quantum state detection device characterized in that the above-described multipole matching detection electrode array is integrally integrated on a surface-electrode Paul trap substrate and forms a microchannel-shaped arrangement along the movement path of the ion-based qubit.
In paragraph 1, A non-destructive quantum state detection device comprising a superconducting shield formed of a niobium (Nb) or niobium-titanium (NbTi) thin film and arranged to surround the outer side of the detection electrode, wherein the superconducting shield blocks external RF noise and simultaneously corrects environmental magnetic field fluctuations by the Meissner effect.
In paragraph 1, A non-destructive quantum state detection device characterized in that the surface of the detection electrode facing the ion-based qubit is composed of single-crystal gold (Au) or a superconducting thin film treated with argon ion beam cleaning, and the anomalous heating rate occurring on the surface is suppressed to 0.1 phonons/ms or less.
In paragraph 1, A non-destructive quantum state detection device characterized in that the control unit includes a Bayesian estimator that receives as input the time domain amplitude sequence and phase sequence of the output signal of the high-sensitivity sensor unit, and the Bayesian estimator classifies the quantum state of the ion-based qubit into one of |0>, |1>, or a quantum superposition state within a single measurement cycle, wherein the classification fidelity is 99% or higher.
In paragraph 1, A non-destructive quantum state detection device characterized in that the electromagnetic trap is a surface-type pole trap operating in a cryogenic environment of 4 Kelvin (K) or less and an ultra-high vacuum environment of 10⁻¹¹ Torr or less, and the ion-based qubit is levitating at a distance of 30 micrometers (μm) to 100 micrometers (μm) from the surface of the surface-type pole trap.
In a method for non-destructively detecting the quantum state of an ion-based qubit, (a) a step of levitating at least one ion-based qubit encoded in a quantum superposition or quantum entanglement state, having different electrostatic multipole moments for the |0> state and the |1> state, within an electromagnetic trap; (b) a step of generating a micro-image charge change induced by the difference in multipole moment between the |0> state and the |1> state at a detection electrode disposed adjacent to the ion-based qubit in a non-contact manner, wherein the resonance frequency of the detection circuit is separated by at least one octave from the secular frequency of the motion mode so that the micro-image charge change is not dependent on the motion mode vibration amplitude of the ion-based qubit; (c) If the detection electrode is composed of two or more divided regions, a step of differentially synchronously detecting the signal of each of the divided regions to cancel out the motion amplitude component and extract only the multipole moment component; (d) amplifying the extracted multipole moment component signal by a high-sensitivity sensor unit operating in a dispersion region where the measurement-induced phase damage rate is 1/10 or less of the intrinsic phase damage rate; and (e) inputting the amplified signal into a Bayesian estimator to determine the quantum state of the ion-based qubit within a single measurement cycle; comprising, A non-destructive quantum state detection method characterized in that no measurement photon energy is applied to the ion-based qubit during steps (a) through (e).
In paragraph 15, A non-destructive quantum state detection method characterized by further including the step of immediately reusing the ion-based qubit in a subsequent quantum gate operation with its motion mode preserved without releasing it from the trap after the determination result of step (e) above is obtained.

Description

Apparatus and Method for Non-mediated Non-destructive Quantum State Detection of Ion Qubits via Motional Modes The present invention relates to the field of quantum computing and quantum information processing technology, and more specifically, to an apparatus and method for directly and non-destructively detecting the quantum state of an ion-based qubit trapped in an electromagnetic trap without the application of photon energy for measurement, by utilizing only the electromagnetic inductive coupling between an electric multipole moment dependent on the internal quantum state of the ion-based qubit and a detection electrode, without mediating the motional mode of the ion-based qubit. Quantum computers are systems that utilize the properties of quantum superposition and quantum entanglement of qubits to process computational problems that cannot realistically be solved by classical computers. Among the various qubit platforms studied to date, trapped ion-based quantum computers are considered one of the most promising quantum computing platforms because the atomic ions themselves possess the same physical properties as in their natural state, single-qubit and 2-qubit gate fidelity reaches over 99%, and coherence time can reach several minutes or more. The standard method for reading out the quantum state of a qubit in a trap-ion quantum computer is state-dependent fluorescence detection. This method determines the qubit state by irradiating an ion with a laser that selectively couples to only one of the two energy levels constituting the qubit, and counting the difference between the emission of multiple fluorescent photons in the bright state and the non-emission of photons in the dark state using a photodetector. Since the fidelity of a single qubit measurement can reach 99.99%, this method is currently adopted as the standard readout technology for commercially available trap-ion quantum computers. However, laser fluorescence detection methods inherently contain several fundamental limitations. First, wavefunction collapse inevitably occurs during the process in which ions absorb and emit photons upon laser irradiation. This means that after measurement, the qubit is projected onto one of the eigenstates |0> or |1>, destroying the quantum superposition information the qubit possessed prior to measurement. Consequently, mid-circuit measurement—which involves checking the qubit state during quantum computation and immediately reflecting the result in the operation—is virtually impossible; even if possible, it requires an additional operation of shuttleing ions to a separate zone for error correction. Second, photon recoil, which occurs when ions absorb and emit photons during the fluorescence process, adds energy to the ions' motion modes, causing motional heating. In trap ion quantum computers, motion modes are a core resource utilized as the quantum bus for 2-qubit gate operations; however, if motion modes are heated after fluorescence measurement, the fidelity of subsequent gate operations may be degraded. To prevent this, an additional sideband cooling process is required after measurement, which increases computational latency. Third, fluorescence detection requires a complex free-space optical system to precisely aim and align a measurement laser beam near the ion. Such an optical system is a fundamental limiting factor in the integration of ion traps and expansion into multi-qubit arrays. In systems with tens or more qubits, precisely aiming individual laser beams at each ion requires extremely complex optical designs and active stabilization systems, resulting in low engineering scalability. Fourth, measurement crosstalk caused by stray photons generated by the measurement laser to adjacent qubits is a serious problem that causes errors during simultaneous reading of multiple qubits. To suppress this crosstalk, the reading area must be partitioned separately or a multilayer optical shielding structure must be designed, which increases system complexity. As a prior art to partially address these issues, a method is known for non-destructively detecting spin states through image current induced in a pickup electrode by utilizing the continuous Stern-Gerlach effect (CSGE), in which the spin state of a single particle finely alters the intrinsic vibration frequency of its motion mode in a Penning trap with a magnetic bottle structure. However, this method has a fundamental limitation in that it necessarily requires a non-uniform magnetic field structure known as a magnetic bottle, and since the coupling between the spin state and the motion mode is formed through the magnetic bottle, qubit state information must be transmitted via the motion mode. Because the motion mode itself changes, the motion mode is disturbed during the measurement process, making it difficult to reuse it as a quantum bus for a subsequent quantum gate. In addition, a hybrid system approach has been proposed to realize quantum sta