Editorial Feature

Advancing Quantum Computing: Overcoming the Challenge of Qubit Instability

Although quantum computing technology is developing quickly, one major obstacle to its full realization is the intrinsic instability of qubits.

Advancing Quantum Computing: Overcoming the Challenge of Qubit Instability

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The field of quantum technology is booming, with the unique laws of quantum physics being used to create new and creative devices. It is dependent upon the peculiar characteristics of subatomic particles, such as entanglement and superposition.

Superposition is the capacity of a quantum system to exist concurrently in two or more states. Entanglement ensures that no matter how far away two quantum systems are, measuring one instantly changes the other. Qubits, the quantum

equivalent of classical computer bits, are used in quantum technology to capitalize on these features.

The qubit is a potent and revolutionary invention, as it can exist concurrently as a 0, 1, or both. This allows for complex computations that consider multiple alternatives simultaneously. Superconductors, trapped ions, neutral atoms, single photon emitters, and photons are the building blocks of quantum technology platforms.

What Are the Challenges in Controlling Qubits?

One of the major challenges in developing quantum technology is maintaining qubits in their desired states long enough to perform computations. Qubits are extremely susceptible to changes in their surroundings.1

For a qubit, quantum coherence is an ideal characteristic. Qubit quality comparisons are based on the coherence time or length of the qubit coherence. Coherence determines a qubit's lifetime because it provides information about how long it maintains information.

Instability and subsequent decoherence of qubits can result from various mechanisms. The main cause of decoherence in quantum systems is their interaction with their surroundings. Temperature swings, stray particles, and electromagnetic fields are common environmental factors that affect qubits.

The quantum system loses its original quantum properties as a result of these interactions. These external factors pose a challenge when performing operations with carefully isolated qubits.

Types of Operational Qubit Instabilities

One type of fault affecting the stability of qubits is dephasing or phase flip error.2 Dephasing usually occurs when a qubit's capacity to maintain its phase is exceeded by the time needed to complete all operations. Environmental noise like electromagnetic waves and cosmic rays can cause phase flips. The gate operations and the crosstalk they cause on nearby qubits are two further sources of dephasing.

As described above, the basic building block of quantum information, a qubit, is frequently described as either 0 or 1, or as being in a superposition of 0 and 1 simultaneously. A qubit's state can also be intentionally flipped from 0 to 1, and vice versa, upon receiving a specific command. However, a type of qubit instability known as a bit flip error may occur when the bit is flipped randomly due to environmental interference.

When quantum gates are used to manipulate qubits, gate operation errors may also occur.

Qubit instability affects quantum sensors, which reduces their accuracy and precision.

Decoherence due to quantum computing instability restricts the time that quantum algorithms can be correctly implemented. The security and dependability of quantum communication protocols, including quantum key distribution, are also affected by qubit instability.

Approaches for Mitigating Decoherence

Researchers are actively exploring methods to reduce the effects of qubit instability. Methods used to increase the performance of quantum technologies and prolong coherence times include dynamical decoupling schemes, environmental shielding, quantum error mitigation, and quantum error correction.

Quantum error mitigation techniques are used to reduce qubit instability of quantum computations.3 This is frequently accomplished by repeatedly running marginally different circuits and post-processing the outcomes in a traditional manner. However, this technique is only viable when limitations in quantum hardware may render full quantum error correction impractical. Quantum error mitigation techniques offer a reduction in instability that may be helpful; however, comprehensive quantum error correction is required for practical processing with numerous qubits.

Quantum error correction is used to find and correct mistakes in quantum computers.4 This algorithm leverages mathematical techniques employed to create classical microprocessors in harsh environments, which are specifically designed to withstand severe interferences, where faults are highly likely to develop.

In quantum error-correcting, for each logical qubit used to perform computations, several physical qubits are designated to store information and correct any arising errors. Distributing the information among several qubits helps protect data and minimize decoherence.

However, a fully functional quantum machine will require scaling to a higher number of logical qubits. As such, the quantum community faces a great challenge in being able to deploy the necessary amount of physical qubits to correct errors.

Ongoing research and development in quantum error correction are providing new insights into extending the coherence times of qubits. For example, combining advances from multiple fields, such as model-free reinforcement learning with superconducting quantum circuits5 and noise-adapted quantum error correction.6

The Future of Quantum Error Correction

Quantum error correction is largely behind the promise of large-scale quantum computing. Within the quickly developing field of quantum technology, quantum error correction is a valuable asset in realizing these sophisticated devices' ability to function. The importance of qubit instability control will only increase as scientists continue to push the limits of quantum technology.

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References and Further Reading

  1. Bhadage, A. (2023). Quantum Decoherence: Unraveling the Loss of Quantum Coherence. [Online] Advanced Physics Academy. Available at: https://www.linkedin.com/pulse/quantum-decoherence-unraveling-loss-coherence-aphysicsacademy-ncfpe/
  2. Boger, Y. (2023) Guest Post: Quantum Error Correction – The Key To Realizing Quantum Computing’s Potential. [Online] The Quantum Insider. Available at: https://thequantuminsider.com/2023/09/08/guest-post-quantum-error-correction-the-key-to-realizing-quantum-computings-potential/
  3. Riverlane. (2022). Quantum Error Correction. [Online] Riverlane. Available at: https://www.riverlane.com/quantum-error-correction
  4. Q-CTRL. (no date). What is Quantum Error Correction? [Online] Q-CTRL. Available at: Q-CTRL https://q-ctrl.com/topics/what-is-quantum-error-correction
  5. Sivak, VV., et al. (2023). Real-time quantum error correction beyond break-even. Nature. doi.org/10.1038/s41586-023-05782-6
  6. Jayashankar, A., Mandayam, P. (2023). Quantum Error Correction: Noise-Adapted Techniques and Applications. J Indian Inst Sci. doi.org/10.1007/s41745-022-00332-x

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Written by

Ilamaran Sivarajah

Ilamaran Sivarajah is an experimental atomic/molecular/optical physicist by training who works at the interface of quantum technology and business development.

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