Since the early 1800s, the scientific community has been learning about quantum mechanics and how their properties impact the physical environment on both a microscopic and macroscopic scale. What sets this new quantum physics apart from classical physics?
Well, for one, in classical physics, the state of a physical system can be predicted, calculated, and measured with 100% certainty following the famous laws derived by physicists such as Newton or Maxwell. In the quantum domain, this is not the case. When it comes to measuring or predicting the quantum state of a particle (such as a photon), one could use a probability distribution function and take a “best guess” but could never know for certain what that state is.
This is the basis of Heisenberg’s uncertainty principle, which was introduced back in 1927 and is essential for a new form of security called quantum cryptography. Additionally, these states can be “superposed” (added together) to form a quantum component called a qubit, or a quantum bit version of a classical bit (0 or 1). This new concept of a quantum bit may be in a superposition of both the 0 and 1 states simultaneously and may not always be in the same state depending on when it is measured.
Furthermore, the amount of information it can manipulate and represent far exceeds that of the traditional binary approach consisting of discrete states 0 and 1. And we’ll see here that the basic unit of quantum information, the qubit, is core to quantum computing systems.
Quantum cryptography finally gives us 100% secure transmission from anywhere in the world
In the past few decades, scientists in both academia and industry have tried coming up with a 100% provable secure system. It turns out that the strange properties of quantum mechanics can be utilized with communication and cryptography protocols. In fact, some major organizations and networks around the world are currently using quantum cryptography to their advantage, including both physically and wirelessly connected networks.
One example of a secure data transferring system utilizing quantum cryptography is called quantum key distribution (QKD). While QKD has multiple protocols, the most popular one used today is BB84, a protocol invented in 1984 that exploits randomized photon polarization and its associated states. Not only does this protocol allow for protected transmission, it also tells the transmitting or receiving end if there are any eavesdroppers. The goal is to create a unique shared key between both transmitting and receiving parties that can be used for encrypting data. Figure 1 demonstrates the BB84 protocol system in which “Alice” is the transmitter and “Bob” is the receiver.
Figure 1: The BB84 protocol system (Image from the book “Optical Wireless Communications” by Alberto Carrasco-Casado, Verónica Fernández, and Natalia Denisenko)
This secret key is produced by both the transmitting and receiving ends using randomization and photon polarization. But the process is not quite that simple. The transmitter starts off by randomizing a bit (0 or 1) but associating it with one of two bases of photon polarization, which is pre-determined by the transmitter. When sending these randomized, polarized states over a quantum channel, the transmitter records the states, their associated bases, and timestamps.
The receiver also uses its own randomized measurement method and notes the photon polarization associated with each basis, along with a timestamp of each bit. When transmission has finished, the receiver will have recorded many measurements in a very specific order and will share its results with the transmitter through some public communication channel. At this point, the transmitter can tell the receiver to discard information that doesn’t align with what it sent, leaving a shared key containing 1’s and 0’s at specific timepoints unique to the receiver and transmitter. And the kicker here is that when performing a measurement of a polarized photon, the photon polarizes to a new value based on your method of measurement. This prevents eavesdroppers from measuring and interpreting information for themselves, as it produces disparities on both ends that are detectable and recoverable.
While cryptography applications with fiber optics use the randomized properties of photons, there have been some recent successful experiments in communication and quantum cryptography that incorporate quantum entanglement, the process of a employing a pair of particles that are closely correlated with each other due to a phenomenon that occurs when they are first generated or interfaced with each other.
But who’s using this method of cryptography and how? While some organizations have already successfully demonstrated quantum cryptography in some optical-fiber networks, academia and technology startups are working to commercialize it. Crypto Quantique is a startup company that is already on its third generation of a crypto chip called the QDSC, or Quantum Driven Secure Chip, and is looking to revolutionize internet of things security. And Nanyang Technological University (NTU), as another example, has developed hardware providing secure, quantum communication that is much, much smaller than those seen in most other applications (Figure 2). It won’t be long until we all have cell phones and tablets that utilize this new and exciting technology.
Figure 2: NTU’s crypto chip is 1,000× smaller than most other configurations. (Image: Nanyang Technological University Singapore)
A new age of computing
But how else can we take advantage of this quantum business? We’re on the brink of taking a light-year-sized step in processing power, and we’re calling it quantum computing. The idea is to incorporate quantum properties, such as superposition, as a means of storing and processing information. Consider the qubit, which can have a state represented by the possible “superposed” point on a sphere’s surface, as seen in the Bloch Sphere in Figure 3. This sphere is a geometrical 3D description of the qubit space and demonstrates how a qubit can be measured as having an up spin or a down spin (north or south pole).
Figure 3: Bloch Sphere representing the pure state of a qubit (Image: Wikipedia)
So far, this is not terribly different than the traditional binary bit state in classic computing. But because we are following the laws of quantum mechanics, we can combine these quantum states to form a composite system, and we see that the amount of basis vectors produced by this system scales exponentially with the number of qubits used.
For example, a 2-qubit system is composed of the spin of two particles and whose quantum state is one of four basis vectors. For 3 qubits, this becomes eight basis vectors; 4 qubits would provide 16 basis vectors, and so on. We now see that for the same capacity as the traditional binary bit state of 0 and 1, we can achieve exponentially higher amounts of states. This is the heart of quantum computing power. However, the algorithms needed to decode, measure, and make use of these states are not trivial.
Google recently announced that their latest quantum computer located in Santa Barbara, California, completed a calculation using 53 qubits in just a few minutes that would have normally taken a modern-day supercomputer thousands of years. And Google’s quantum computing rival, IBM, has made a quantum computer and software toolset publicly accessible for anyone to develop and test code using their cloud-based software, Qiskit and Circuit Composer (Figure 4).
Figure 4: IBM’s Circuit Composer, a graphical quantum programming tool (Image: IBM Quantum Experience)
While these two high-profile companies are competing for quantum computing supremacy, they aren’t the only ones in the race. Many tech startups are taking a shot at providing quantum computing hardware and software services. According to Quantum Computing Report, at least 156 companies are working toward commercializing something related to quantum computing. As an example, the first company on this list is 1Qbit, a Canada-based startup that had recently partnered with Microsoft and others on providing a full-stack, open-cloud ecosystem bringing quantum computing to people and organizations around the world. A few companies down the list is Aliro Quantum, a Massachusetts-based startup that formed only last year that has already made significant headway on providing hardware-independent toolkits for developers of quantum algorithms and applications. While most of the companies on the list focus on software-specific solutions, plenty are developing hardware as well. But what do all of these companies have in common? They’re working to provide a simple commercial-scale solution that solves enormously large problems.
It’s exciting to think of what quantum technology will be available in the coming years, and while it’s easy to get lost trying to understand the quantum realm, the practical uses for it have proven to be nothing less than astounding.
