Well, the quantum computers that you will find in usage right now use Josephson contacts for that:

https://en.wikipedia.org/wiki/Superconducting_quantum_computing

Advantage: it has been proven to work, QCs are heading towards three-digit Qubit numbers. Disadvantage: requires ultracryogenic temperatures probably disqualifying it from mass production.

Another concept would be ion traps:

https://en.wikipedia.org/wiki/Trapped-ion_quantum_computer

Advantage: should be easier scalable, disadvantage: decoherence and perturbing interactions

The third system is the usage of well-defined defect centers, particularly the NV center in diamond:

https://thequantuminsider.com/2022/03/31/5-quantum-computing-companies-working-with-nv-centre-in-diamond-technology/

https://en.wikipedia.org/wiki/Nitrogen-vacancy_center#Applications

Advantage: longest coherence times, in good enough crystals potentially up to the second range at room temperature; disadvantage: spins are harder to address (but our colleagues are working on it)

Dear Ali Amiri

You may find useful information presented below:

Quantum computing, which relies on the principles of quantum mechanics and uses qubits as its basic units of information, is an area of active research and development. There are several practical directions in qubits experimental implementation. As of my last knowledge update in January 2022, ongoing advancements in the field include:

Advancements in experimental implementations of qubits are crucial for achieving the milestones in quantum computing, such as quantum supremacy and fault-tolerant quantum computation. Researchers and engineers are continually exploring new materials, techniques, and architectures to improve the coherence, fidelity, and scalability of qubits in quantum computing systems. Keep in mind that the field is rapidly evolving.

Kubitler karbon atomunun veya diğer atomların fiziksel ve kimyasal özellikleri dikkate alınarak belirlenen yapılardır. Bu durumda en kararlı olan karbon yapısındaki grafit yapılı elektriği ileten elmastır. Elmas, en kararlı yapıdadır. Bütün atomların atomik yapısı köşegenlerindeki atomların kararlı, sağlam, fiziksel ve kimyasal özelliklerine bağlıdır. Buna en iyi örnek karbonun elmas yapısı olur.

Implementing qubits and quantum logic gates physically involves building a quantum system that can manipulate and store quantum information. Currently, several physical implementations of qubits exist, each with its own set of advantages and challenges. The most common physical implementations include superconducting circuits, trapped ions, and topological qubits. Here, I'll provide a general overview of how qubits and quantum logic gates can be implemented:

1. Superconducting Qubits:

• Physical Basis: Superconducting qubits use superconducting circuits, typically Josephson junctions, to create artificial atoms. The two lowest energy states of the superconducting circuit represent the qubit states (|0⟩ and |1⟩).
• Quantum Logic Gates: Microwave pulses are used to manipulate the state of the superconducting qubit, implementing operations analogous to classical logic gates. The controlled-NOT (CNOT) gate is a fundamental quantum logic gate.

2. Trapped Ions:

• Physical Basis: In trapped ion quantum computers, individual ions are trapped and manipulated using electromagnetic fields. The internal electronic states of the ions serve as qubit states.
• Quantum Logic Gates: Quantum gates are implemented by applying laser pulses to induce transitions between different internal states of the trapped ions. Techniques like entanglement through controlled operations are used.

3. Topological Qubits (e.g., Majorana Qubits):

• Physical Basis: Topological qubits rely on anyons, special types of particles that exist in certain materials. Majorana fermions are an example of anyons.
• Quantum Logic Gates: Braiding operations, where anyons are exchanged in a specific way, can be used to perform quantum gates. The braiding of Majorana fermions, for instance, can be used to implement a universal set of quantum gates.

4. Quantum Dots:

• Physical Basis: Quantum dots are semiconductor structures that can trap individual electrons. The spin states of these electrons can be used as qubits.
• Quantum Logic Gates: Quantum dots can be manipulated using electric fields and can be used to implement single-qubit and two-qubit gates.

5. Photonic Qubits:

• Physical Basis: Quantum information is encoded in the properties of photons, such as polarization or the presence/absence of a photon.
• Quantum Logic Gates: Linear optical elements like beam splitters and phase shifters can be used to implement quantum gates. Quantum information is typically manipulated through photon interference.

General Challenges:

• Decoherence: Quantum systems are susceptible to environmental interactions that can cause loss of coherence. Techniques like error correction are being developed to mitigate this issue.
• Scalability: Building large-scale, fault-tolerant quantum computers remains a significant challenge.

Building a quantum computer involves combining these physical qubits with techniques to control and entangle them effectively, as well as minimizing errors through error correction. It's important to note that the field of quantum computing is highly dynamic, and advancements are occurring rapidly. Researchers are exploring various physical implementations to overcome existing challenges and build practical quantum computers.The physical implementation of qubits and quantum logic gates depends on the technology used. For example, IBM has chosen to build superconducting transmon qubits which are controlled through microwave pulses. By varying the amplitude and shape of the pulses, they are able to implement the specified gates 1.

Another example is the use of ultracold trapped ions to store each qubit in the state of an ion. Ions interact strongly via their mutual Coulomb repulsion, thus allowing unitary manipulation of the qubits’ joint state to be achieved with lasers 2.

There are many other ways to manipulate qubits in the physical world, such as using polar molecules in pendular states 3.

I hope this helps!

Quantum logic elements include quantum qubits. For example, photon qubit consists of two or four polarized and antipolarized photons which are running through the silicon nanowires. The pair of these photons realizes a photon qubit.