DiVincenzo's Criteria for absolute beginners
Day 13 — Quantum30 Challenge
Imagine you’re embarking on the journey to create your own quantum computer. You’ve successfully developed qubits, the building blocks of quantum computation, and a system to manipulate them. However, merely having these components doesn’t instantly qualify your creation as a quantum computer.
To ensure its functionality, you need to subject it to a set of criteria known as DiVincenzo’s criteria. These criteria are carefully designed benchmarks that test the capabilities of your quantum system for both computation and communication.
Criteria for Quantum Computation
1. A scalable system with well-defined qubits
Let’s break this down into two
a) Well-defined qubits:
Until now, we know a qubit is a two-level state. It can take the values (|0>,|1>), (|g>,|e>), (|up>, |down>), etc. depending on what parameter of the quantum particle you are using. These qubits naturally have the ability to undergo superposition and entanglement. A well-defined qubit is one which can remain in the superposition during computations, calculations, or operations without collapsing. It will collapse only when the measurement is performed on it.
b) Scalable system:
A scalable system means a system that can occupy and control a lot of qubits without destroying or collapsing the qubits state. Currently, with the technology we have, a system of creating well-defined qubits is a challenge. This is due to the large experimental setups it requires. Also, this does not guarantee that all the qubits will remain their ‘well-defined-ness’. One could say that as the number of computational qubits increases they become less well-characterized until a threshold is reached at which they are no longer useful.
2. Initialising qubits to desired states
I should be able to set my starting state according to my needs during computation. There are various methods to initialize like cooling, pumping, etc. to get to a specific state. Once the qubits are initialized, they are ready for further computations.
3. Long coherence times
Coherence means the ability of a quantum particle/ system to remain in a superposition state. Decoherence, on the other hand, is when the quantum state collapses and loses its quantum behavior. For a quantum computer, we want to have a longer coherence duration as that is the only state where we can perform various operations, calculations, etc. As we can infer from point one, decoherence can be a challenge for huge quantum systems.
4. Universal Set of Quantum Gates
Universal means that a limited number of gates can be used to perform different computations. For example, in classical computing, NAND and NOR gates are called Universal because other gates AND, OR, NOT, etc. and thus, computations can be made by different combinations of these two gates.
So, a universal set of quantum gates simply means, a specific set of quantum gates/ operations, when in various combinations, can perform different quantum computations. CNOT gate is an example of universality which creates entanglement between two qubits.
5. Qubit-specific measurement capability
Measurement is the final step in any computation which tells whether the result is right or not. For quantum computers, the measurement system should be qubit-specific and high fidelity. Qubit-specific means that I can measure any qubit or set of qubits I want. Fidelity means how accurately we can measure the state. Measurements can be accurate but sometimes, if it is not, we repeat to increase the success rates.
Criteria for quantum communication
1. Interconversion of stationary and flying qubits
In classical computers, the conversion of human-readable to computer-readable (binary) and vice-versa takes place for communication. Similarly, in the quantum realm, there are two types of qubits used for communication
a) Stationary qubits:
These are Quantum bits that are localized and held at fixed position within a physical system (eg: trapped ions, neutral atoms, superconducting circuits, etc). They are well-isolated from the environment to maintain coherence for longer duration of time and are used for quantum computations.
b) Flying qubits:
These are the qubits thatare carried by particles that can move freely (photons, electrons, etc.). Because they can travel, the are able to transmmot the quantum information over long distances enabling the creation of quantum communication links and quantum networks.
Interconversion refers to the ability to transform quantum information between theses two forms and thys allows information to be moved between different locations.
2. The ability to faithfully transmit flying qubits between specified locations
We want to ensure that the quantum information carried by flying qubits reaches its destination without getting messed up. Faithfully transmitting means maintaining the quantum properties during transmission.
The above criteria are the reason why quantum communication is not as widespread or commonly implemented as quantum computing. There are possibilities of the qubit to entangle with the flying qubit which can be either helpful or dangerous. In this field, managing and controlling this entanglement is both challenging and crucial.
Quantum communication is advancing, we already have certain methods like Quantum Key Distribution (QKD), Quantum Cryptography which provides unbreakable encryption.
Conclusion
As one navigates the intricate domain of quantum computing and communication, it’s crucial to recognize that these criteria serve as a roadmap, guiding progress toward harnessing the immense power of the quantum realm. Overcoming challenges and aligning with these benchmarks holds the potential for revolutionary breakthroughs in computation and communication.
References
Article as a part of QuantumComputingIndia’s challenge.