Entangled and shuffled

What makes quantum particles and systems different from normal objects?

What is Quantum Information Science (QIS)?

The field of Quantum Information Science (QIS) is a multidisciplinary area of research that is positioned right in between science, engineering and technology. It studies how we can take advantage of the unique properties of quantum systems for technological and informational applications such as creating new and better computers, developing digital networks with better encryption protocols, and creating sensors and measuring devices with enhanced precision.

Why is QIS important?

During the last century, the development of lasers and transistors led to an explosion in the availability of technology and information circulating around the world. This has strongly reshaped our societies, defining a new “information age.” Effectively, all the information and data that we use is currently stored, transmitted and processed through standard ("classical") methods that involve the manipulation of electronic states that are interpreted as “ON” or “OFF,” "0" or "1" – states of information known as bits.

The complexity of these information systems is not a feature of the fundamental parts of our computers, but rather only a result of the enormous scale of both the number and speed at which bits are processed in our devices. A significant challenge, however, relies on the fact that the amount of memory and processing power required to handle and analyze large systems scales exponentially. This means that as our information systems keep expanding, the amount of resources required to run these systems will become unsustainable in the long term. The hope is that QIS can provide a solution to this problem.

What distinguishes quantum technologies from regular devices?

We can identify three “ingredients” that distinguish quantum technologies from regular devices:

1) Superposition: While a bit can have a value of either zero or one, a quantum bit (qubit) can have a value that is either zero, one or a quantum superposition of these values. In a state of superposition, the value of the qubit cannot be described as either zero or one in a definite way. Given two bits, a regular computer can store four possible different values (zero zero, zero one, one zero, or one one), although only one of those at a time. Given two qubits, in principle all four values can be represented simultaneously. Mathematically, we represent this as:

|⟩=a|00⟩+ b|01⟩+c|10⟩+d|11⟩

Each bracket |⟩ (“ket” for short) represents a state on which the system can be, and the fact that they are added together indicates the superposition.

2) Correlations: the state of a qubit can be readily affected by its interaction with other elements in the system, influencing the probability of a certain outcome during experiments. Given the right circumstances, a particular combination of states might prevent certain outcomes through destructive quantum interference.

3) Entanglement: Entanglement is a stronger, more specific form of correlation where particles are linked in a way that their fates are intertwined, even when separated by large distances. When qubits become entangled, they form a “global” system such that the quantum state of different parts of the system cannot be described independently. We therefore say that there exist specific correlations between each of the components.

A key insight to understand the advantages of quantum systems consists in realizing the similarity between the superposition of quantum states (|00⟩+ |01⟩+ |10⟩+… ) and the way a classical parallel computer runs, where many different inputs are processed within the time of a single calculating cycle. However, unlike the stack of Central Processing Units that is necessary to run a classical parallel computation, a single quantum system has the potential to provide parallel processing as a “built-in” feature. Initially, this suggests the possibility of carrying out these calculations with a much smaller number of resources and a method to bypass the exponential explosion problem.

How can we use tabletop games to explain QIS?
Given that studying quantum systems is both technically and conceptually challenging, QIS topics and concepts are not usually discussed until students take advanced undergraduate and graduate level classes. However, it is possible to highlight the key differences between classical and quantum systems by using items commonly found in tabletop games such as cards. We think the fact that these items are easily accessible should help to make the quantum concepts more relatable to young students and a general audience.

• If two particles that have a spin sum of zero have “hidden variables” that can describe their spin before the measurement, then there’s a known limit to how often we can measure both of the particles as having a positive spin (on any axis… any axis??)

Teacher tips:

• Suggested STEP UP Everyday Actions to incorporate into the activity.
• Consider using whiteboards during discussions, so students have time to brainstorm and work through their ideas before saying them out loud.
• As students experiment, roam around the room to listen in on discussion and notice experiment techniques. If needed, stop the class and call over to a certain group that has hit on an important concept.
• Consider these responsive tools and strategies and/or open ended reflection questions to help push student thinking, and to help students track their thinking during the activity.
• Connect to students’ lives and create opportunities to develop STEM identity using these suggested extensions.
• Allow the work of physicists to come alive by signing up for a virtual visit from a working physicist using APS’ Physicist To-Go program. You can request a quantum physicist to talk about the concepts students learned in this activity!

• There are also many STEM YouTube channels that are great for learning about QIS such as Looking Glass Universe, Qiskit. and AM.
• Sign up for Physicists To-Go to have a scientist talk to your students.
• Use Elisa Torres Durney’s scientist profile to spark conversations about who does quantum physics.

Real world situations/connections can be used as is, or changed to better fit a student’s own community and cultural context.